I would think at least 10 days and that may be to early so try 12....
IUI pretty much is the same thing as regular. Sperm still have to meet the egg and the egg has to travel down and implant. The only difference is the trigger shot. Depending on the amount it can take up to 10 days to get out of your system. I'd do an hpt on 8 or 9 dp trigger and see if is bfn so when you test a few days later, if you get a bfp you'll know isn't left over trigger :)