How to add minutes to the time part of datetime
Use DATEADD
:
SELECT DATEADD(mi, @increase, @shift_start_time);
db<>fiddle demo
Using dateadd:
DATEADD(minute,@increase,@shift_start_time)
the first argument can be chosen among: year quarter month dayofyear day week weekday hour minute second millisecond microsecond nanosecond
please check https://learn.microsoft.com/en-us/sql/t-sql/functions/dateadd-transact-sql?redirectedfrom=MSDN&view=sql-server-ver16