IUI done after follicle rupture. Later?

Dear doctors, i have been on letroz 2.5 mg bid since 2nd day of period for 5 days. I have been on follicular scanning since day 8 since we are going for iui this time . Trigger shot was given when my follicle size is at 22mm on day 12 and doctor said we will go for double iui later . Today again we did scan and my follicle size is 27 mm and doctor said single iui is fine no need for double iui as she is confident it will rupture next day and single iui is fine . Is iui done before follicle rupture or after? And 27mm is an over mature follicle ? I read in Practo reports that some doctors saying it's a cyst and generally 22 mm is an ideal size? Is the over mature follicle due to letroz? Also is iui done before follicle rupture or later?