Try like this
$stat='sys.osuptime.latest'
$now=Get-Date
$vms=Get-VM
Get-Stat-Entity$vms-Stat$stat-Realtime-MaxSamples1|
Select @{N='VM';E={$_.Entity.Name}},
@{N='LastOSBoot';E={$now.AddSeconds(-$_.Value)}},
@{N='UptimeDays';E={[math]::Floor($_.Value/(24*60*60))}} |
Export-Csv-Path.\report.csv-NoTypeInformation-UseCulture