It would be better to separate the time-zone logic to a separate unit and test just this logic.
This logic is simply convert minutes to HH:MM, the source of time-zone is from date object...
Date filter now supports:
yyyy: four digit year
yy: two digit year
MM: two digit month
dd: two digit day of month
HH: two digit hour in 0-23
KK: two digit hour in 0-12
mm: two digit minute
ss: two digit second
a: am/pm
Z: four digit timezone offset
example {{ timestamp | date:'yyyy-MM-dd HH:mm:ss' }} becomes 2010-10-13 14:45:23
