Can you ovulate before trigger on Follistim cycle?

Going in for 3rd IUI on Tuesday!

We have been doing Follistim and have to do trigger shot on day 14 and iui day 16. iui was originally set for monday but got pushed back because doc wanted my 2 eggs a little more mature.

When i look at when i would normally ovulate on my period tracker app without meds, it shows tomorrow (sunday) is when i would ovulate.

Does Follistim push back ovulation? Will triggering tomorrow night(sunday) be to late for Tuesday IUI?

I just had U/S today so im guessing the doctor would have been able to see when i was about to ovulate? Has anyone done IUI day 16 before on Follistim cycle?