One of the most important things you should do to your systems is to ensure they have the right time.
In this post I will show how to check and ensure your systems have the correct time using PowerCli.

==> Login to vCenter:

$admin = Get-Credential –Credential EXAMPLE\john
Connect-VIServer -Server vc.example.com -Credential $admin

==> Check time settings:

Get-VMHost | Sort Name | Select Name, `
   @{N="NTPServer";E={$_ |Get-VMHostNtpServer}}, `
   Timezone, `
   @{N="CurrentTime";E={(Get-View $_.ExtensionData.ConfigManager.DateTimeSystem) | Foreach {$_.QueryDateTime().ToLocalTime()}}}, `
   @{N="ServiceRunning";E={(Get-VmHostService -VMHost $_ |Where-Object {$_.key-eq "ntpd"}).Running}}, `
   @{N="StartUpPolicy";E={(Get-VMHostService -VMHost $_ |Where-Object {$_.Key -eq "ntpd"}).Policy}}, `
   @{N="FirewallException";E={$_ | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Select-Object –ExpandProperty Enabled}} `
   | Format-Table -AutoSize

Output:

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMHost | Sort Name | Select Name, `
>>    @{N="NTPServer";E={$_ |Get-VMHostNtpServer}}, `
>>    Timezone, `
>>    @{N="CurrentTime";E={(Get-View $_.ExtensionData.ConfigManager.DateTimeSystem) | Foreach {$_.QueryDateTime().ToLocalTime()}}}, `
>>    @{N="ServiceRunning";E={(Get-VmHostService -VMHost $_ |Where-Object {$_.key-eq "ntpd"}).Running}}, `
>>    @{N="StartUpPolicy";E={(Get-VMHostService -VMHost $_ |Where-Object {$_.Key -eq "ntpd"}).Policy}}, `
>>    @{N="FirewallException";E={$_ | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Select-Object -ExpandProperty Enabled}} `
>>    | Format-Table -AutoSize
>>

Name                 NTPServer 					TimeZone CurrentTime         ServiceRunning StartUpPolicy FirewallException
----                 --------- 					-------- -----------         -------------- ------------- -----------------
esx1.example.com           					UTC      6/7/2015 3:25:39 PM          False off                       False
esx2.example.com           					UTC      6/7/2015 3:25:40 PM          False off                       False
esx3.example.com 	{192.168.10.1,192.168.11.1}	        UTC      6/7/2015 3:25:42 PM          False off                       False
esx4.example.com 	192.168.11.1 				UTC      6/7/2015 3:25:43 PM          False off                       False

==> Set time to correct time:

// Get time from the machine running PowerCli
$currentTime = Get-Date

// Update time on ESX hosts
$hosts_time = Get-VMHost | %{ Get-View $_.ExtensionData.ConfigManager.DateTimeSystem }
$hosts_time.UpdateDateTime((Get-Date($currentTime.ToUniversalTime()) -format u))

==> Remove old NTP servers (if any):

$old_ntp_server = '192.168.10.1'
Get-VMHost | Remove-VmHostNtpServer -NtpServer $old_ntp_server -Confirm

Output:

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMHost | Sort Name | Select Name, `
>>    @{N="NTPServer";E={$_ |Get-VMHostNtpServer}}, `
>>    Timezone, `
>>    @{N="CurrentTime";E={(Get-View $_.ExtensionData.ConfigManager.DateTimeSystem) | Foreach {$_.QueryDateTime().ToLocalTime()}}}, `
>>    @{N="ServiceRunning";E={(Get-VmHostService -VMHost $_ |Where-Object {$_.key-eq "ntpd"}).Running}}, `
>>    @{N="StartUpPolicy";E={(Get-VMHostService -VMHost $_ |Where-Object {$_.Key -eq "ntpd"}).Policy}}, `
>>    @{N="FirewallException";E={$_ | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Select-Object -ExpandProperty Enabled}} `
>>    | Format-Table -AutoSize
>>

Name                 NTPServer 	TimeZone CurrentTime         ServiceRunning StartUpPolicy FirewallException
----                 --------- 	-------- -----------         -------------- ------------- -----------------
esx1.example.com           	UTC      6/7/2015 3:25:39 PM          False off                       False
esx2.example.com           	UTC      6/7/2015 3:25:40 PM          False off                       False
esx3.example.com 		UTC      6/7/2015 3:25:42 PM          False off                       False
esx4.example.com		UTC      6/7/2015 3:25:43 PM          False off                       False

==> Change NTP to desired configuration:

$ntp_server = '192.168.10.1'
Get-VMHost | Add-VMHostNtpServer $ntp_server
Get-VMHost | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Set-VMHostFirewallException -Enabled:$true
Get-VMHost | Get-VmHostService | Where-Object {$_.key -eq "ntpd"} | Start-VMHostService
Get-VMhost | Get-VmHostService | Where-Object {$_.key -eq "ntpd"} | Set-VMHostService -policy "automatic"

Output:

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> $ntp_server = '192.168.10.1'
PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMHost | Add-VMHostNtpServer $ntp_server
192.168.10.1
192.168.10.1
192.168.10.1
192.168.10.1

==> Enable Firewall Exception

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMHost | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Set-VMHostFirewallException -Enabled:$true

Name                 Enabled IncomingPorts  OutgoingPorts  Protocols  ServiceRunning
----                 ------- -------------  -------------  ---------  --------------
NTP Client           True                   123            UDP        True
NTP Client           True                   123            UDP        True
NTP Client           True                   123            UDP        False
NTP Client           True                   123            UDP        False

==> Start NTPd service

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMHost | Get-VmHostService | Where-Object {$_.key -eq "ntpd"} | Start-VMHostService

Key                  Label                          Policy     Running  Required
---                  -----                          ------     -------  --------
ntpd                 NTP Daemon                     on         True     False
ntpd                 NTP Daemon                     on         True     False
ntpd                 NTP Daemon                     off        True     False
ntpd                 NTP Daemon                     off        True     False

==> Ensure NTPd service starts automatically (via policy)

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMhost | Get-VmHostService | Where-Object {$_.key -eq "ntpd"} | Set-VMHostService -policy "automatic"

Key                  Label                          Policy     Running  Required
---                  -----                          ------     -------  --------
ntpd                 NTP Daemon                     automatic  True     False
ntpd                 NTP Daemon                     automatic  True     False
ntpd                 NTP Daemon                     automatic  True     False
ntpd                 NTP Daemon                     automatic  True     False

==> Verify all is set the way you expected

Get-VMHost | Sort Name | Select Name, `
   @{N="NTPServer";E={$_ |Get-VMHostNtpServer}}, `
   Timezone, `
   @{N="CurrentTime";E={(Get-View $_.ExtensionData.ConfigManager.DateTimeSystem) | Foreach {$_.QueryDateTime().ToLocalTime()}}}, `
   @{N="ServiceRunning";E={(Get-VmHostService -VMHost $_ |Where-Object {$_.key-eq "ntpd"}).Running}}, `
   @{N="StartUpPolicy";E={(Get-VMHostService -VMHost $_ |Where-Object {$_.Key -eq "ntpd"}).Policy}}, `
   @{N="FirewallException";E={$_ | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Select-Object –ExpandProperty Enabled}} `
   | Format-Table -AutoSize

Output:

PowerCLI C:\Program Files\VMware\Infrastructure\vSphere PowerCLI> Get-VMHost | Sort Name | Select Name, `
>>    @{N="NTPServer";E={$_ |Get-VMHostNtpServer}}, `
>>    Timezone, `
>>    @{N="CurrentTime";E={(Get-View $_.ExtensionData.ConfigManager.DateTimeSystem) | Foreach {$_.QueryDateTime().ToLocalTime()}}}, `
>>    @{N="ServiceRunning";E={(Get-VmHostService -VMHost $_ |Where-Object {$_.key-eq "ntpd"}).Running}}, `
>>    @{N="StartUpPolicy";E={(Get-VMHostService -VMHost $_ |Where-Object {$_.Key -eq "ntpd"}).Policy}}, `
>>    @{N="FirewallException";E={$_ | Get-VMHostFirewallException | where {$_.Name -eq "NTP client"} | Select-Object -ExpandProperty Enabled}} `
>>    | Format-Table -AutoSize
>>

Name                 NTPServer  TimeZone CurrentTime         ServiceRunning StartUpPolicy FirewallException
----                 ---------  -------- -----------         -------------- ------------- -----------------
esx1.example.com 192.168.10.1 UTC      6/7/2015 3:34:49 PM           True automatic                  True
esx2.example.com 192.168.10.1 UTC      6/7/2015 3:34:51 PM           True automatic                  True
esx3.example.com 192.168.10.1 UTC      6/7/2015 3:34:52 PM           True automatic                  True
esx4.example.com 192.168.10.1 UTC      6/7/2015 3:34:54 PM           True automatic                  True