Last call expiry calculations need to be normalized

[rjsparks]

Right now, last calls expire at midnight US Pacific (following whatever daylight-savings is in effect) - at least that's when the document state is changed and a message is sent saying the last call expired.

It should be "when it's that date anywhere on earth" per community discussions about deadlines.

Currently calculations are in more than one place in the code, and they are not calculating the end edge the same way. This should be moved to having the calculation in one place, and it should follow the AoE principle.

cc: @wkumari