Date Math for a user's local time

OK, I'm loosing my mind with date math.

We have a requirement that we need to know if a user clicked a button before or after a date time which is set in a constant.  The date time that the user clicked the button must be localized to them based on their appian profile timezone.

For example:

System default is MST

User is EST

Cutoff is Jan 1st at midnight.  This would apply to every year.

So if they click the button at its 12/31 11:59 PM their local time (EST) then they are before the cutoff.  If they click the button at 1/1/ 12:00 AM their local time (EST) then they are after the cutoff.

I'm trying to use a combination of todatetime, offsetfromgmt gmt and usertimezone, but I'm loosing my mind.

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