You should be able to extract date and time information with something like this (assuming you have PowerShell v3 installed):
$file = "$env:windir\syswow64\ccm\logs\inventoryagent.log"
$pattern = 'SinvEndpoint.*<time="(.*?)" date="(.*?)"'
$Sinv = Select-String $pattern $file | select -Last 1 | % {
$_.Matches.Groups[2].Value + ' ' + $_.Matches.Groups[1].Value
}