Quicksight - Best way to shift time by timezone and assign to shift?

I have a timestream table that has timestamps in GMT. I need to do two things with this time:

1. Shift it to my timezone.
2. Determine what shift the timestamp happened in.

It looks like there is an Excel like ifelse() statement. I have 22 different shifts to examine for. Those cascading ifelse() will get quite complicated. Is there a better way of doing this?