Time Zone Calculations

I am trying to calculate the time in a different timezone. Montreal in my specific case. I have seen various post and have an expression that works - most of the time. For a number of hours - seems to be around 0 UTC the time on the watch doesn’t display correctly. Well it works on the Facer Creator (online) but not on the watch. Please see the images below.

This is the expression I am using:
$((#DUHZ#-5+floor((#DUmZ#+00)/60))%24)<0?24+((#DUHZ#-5+floor((#DUmZ#+00)/60))%24):((#DUHZ#-5+floor((#DUmZ#+00)/60))%24)$:#DUmZ#

(note that Montreal is UTC -5). Any ideas will be welcome.

regards

jcb