how long does it take for the insomnia to go away?

i got taken off of regular melatonin a while back because my insomnia had significantly improved, even when i accidentally skipped a dose or forgot to tell my psych that i'd ran out (don't worry i'm gonna be way more consistent with citalopram lol).

it's day five for me and since starting citalopram, i've not been able to sleep before 2am. it's currently 3am and i need to get up in 2 hours so i've decided a one off all-nighter won't be the end of the world, but i can't really keep this up all the time.

if anyone here experienced insomnia as a side effect, how long did it take to go away? is it worth asking for a short term insomnia medication in the meantime, or should i just wait it out?

thank you in advance :)