...or, to look at it another way, at least 15 hours instruction. I've heard this quoted as 10 hours sim plus 5 hours flight. I guess you'd still need to do the type rating as well (assuming you don't already have it), so add another 5 or 8 hours flight time (depending on whether you have a twin rating already or not). However, many people find the JAA IR course to be so different from the FAA one, that they end up needing rather more than minimums to get up to test standard.
Currently, CAPT is the only school I'm aware of doing IR(H)-only exams (i.e. not as part of an ATPL course).