I don't know if this will work with a (NILE) map - so () are mainly left out.
It starts 60 seconds after the first player enters the game and has one chance in 30 of repeating every 42 seconds.
if past 60 and elapse 42 and random 30 then
flash()
endif
if chain 1 and never then
wind 55,12
endif
BTW
You can adjust the random factor to any number that suits you.