You’ll have to loop them, but all WMI objects in PowerShell have a helper method, so you don’t necessarily need to use that class. Assuming $var contains a property MyDate:
foreach ($thing in $var) { $var.ConvertToDateTime($var.mydate) }
In v3+, you can also switch to using CIM – those tend to return a normal DateTime rather than the underlying WMI weirdo date.