How to trigger before first market from My Markets

Hi,
I have trigger to set user variable when first market from My Markets start (Global Current Time is between mr_1_event_start_timestr and mr_2_event_start_timestr) and it works.
But I'd like to set this user variable between 2 min and 0 min before start of first market from My Markets. 
I tried with condition Global Current Time is between mr_1_event_start_timestr - (1/1440) and mr_1_event_start_timestr - but this is not working...
What should be the correct syntax in the trigger conditions editor?

Hi
_timestr returns a string so cant do proper calculations on a string
 
use this condition instead:
selections trigger expression (mr_1_event_start - now_time)/mf_minute is less than 2

if you put
(mr_1_event_start - now_time)/mf_minute
into the variable viewer or an engineer mode cell you will see the countdown clock to event_start in minutes

Thank you!