Mine lingers in some form right up to the 4 hours mark most times. That's the magic of modern chemistry- just because you finish doesn't mean the penis does...
If your lasted an hour and a half, then congratulations on a successful injection. That's about
the right time for the average Joe. Anything beyond that indicates you need to work on the formula to get it down to that.
If at the 3 hour mark, if it is still almost as erect/stiff/hard as it was at it's best, then I would consider taking Sudafed to help it along its way to going down. If after taking Sudafed and an hour later it hasn't begun to drop, then consider a trip to get some medical help. Personally, not advice to anyone else here, but my doc told me if it had gone to half erect by the 4 hour mark then it would be getting enough blood flow to stop damage. But that's a risk I have to take. Don't do as I do.... So far the Sudafed has worked for me. The real stuff, not the new and improved non-ephenerine stuff. Also, keep your hands off it after you are done using it. Any further stimulus to it by hand will make it stiffen again, so once done, don't touch, in any form.
As has been mentioned here many times, finding the right amount and the right length of time is a process of experimentation. It may take 10 or 20 times to dial it in where it works safely and consistantly for you.