2nd iui

So I have my second iui this week... iui is scheduled for Thursday (16th July). I have to take my shot tomorrow night. The nurse told me to have sexual intercourse tomorrow night after the shot and then take a break for one whole day on Wednesday and Thursday morning I have to bring semen sample for my iui.

I am confused... I thought we have to wait and not have any sexual intercourse before iui so the volume of semen would be greater for the treatment.

What do you all think?