I'm not quite sure what to tell you - each Dr. seems to calculate a different time. Most of them do it at 36 hours after HCG.
I would give yourself the shot at the latest time possible - 9 or even 10:00, in fact.
IUI procedure for washing sperm makes the sperm only live about 6-10 hours in the uterine cavity. My idea as to why they are doing your IUI at 40 hours after HCG is that they probably want to make sure that there is an egg waiting up there for the fresh cleaned sperm since the sperm can not hang out there all daying waiting for ovulation.
My dh and I have had intercourse as well after the IUI proceedure - just to cover our basis. I'll stop at that though, since we did not concieve after we had done 3 IUI's, however, we are going to do another WITH injections of Perganol next cycle, ttc#2
GOOD LUCK! Eager to hear how everything goes!
HCG timing 
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