Hmm... Same timezone as me!
Your probably not using the correct functions. Check the SWQL SDK reference guides and check into
GetUtcDate (instead of GetDate)
or possibly even
A little correction in how your doing your query should accommodate for the timezone problems you're having...
I see on the SDK on page 29 it does say UTC.
Here is the code for reference.
Invoke-SwisVerb $swis Orion.Nodes Unmanage @("N:$nodeid ",$now,$later,"false") where in this case $now and $later are listed below
$now = Wednesday, January 7, 2015 7:29:19 AM
$later = Wednesday, January 7, 2015 2:35:19 PM