I think the answer is 21!
To fly the IR test you need to have completed your MEP training which is 6 hours (There is no requirement for you to have done your MEP test before the IR test, just the training)
And depending on your schools JAR approval (mine was 40hours sim and 15 on the A/C) the minimum time on multi aircraft is 15 hours.
...I think!!!! hope that helps.