Event Log time when Computer Start up / boot up

EventViewer ( System Log )

6009 and 6005 same time stamp, system just started.

6013 - system has been up for a day or more, time in seconds.

6006 - the system was rebooted or shutdown.

PowerShell: Get All Reboot Messages in the Last Month

Get-EventLog -LogName System -After $(Get-Date).AddMonths(-1) | Where { 6009,6005,6006 -contains $_.EventID}