I have tried this (although I wouldn't advise anyone to try it unless they really need it). I took it about 20 minutes before the deed and stayed rigid for a good hour-hour and a half. For the blue pills to work, you do need to be psychologically aroused so don't expect a result if you're not in the mood.
Do note however, this was initially created to help deal with heart conditions; it was only when the side effects were found that it was manufactured for erectile dysfunctional problems, so I would advise you not to take it should you have any heart related illnesses or problems with blood pressure.
Please do your homework before you try it.