the initial ir is the hardest. after that the renewals are fairly straight forward. between initial ir and renewal i hadn't even done any single engine ir flying let alone touch a twin. i spent 2 hours in a fnpt1 sim and then did the test. i actually think i did better on the renewal than on the initial, as i was much more relaxed as i knew the examiner fairly well and had flown with him before. Didn't have to fly into class A airspace, didn't have to fly to another airfield. Did the departure went up to 4500' did a little bit of the enroute section, then went straight into the g/h part of it then straight into the hold for 2 approaches (ndb and ils) and some single engine work. There were less screens up and much more friendly chatter.
Obviously it depends on your personal requirements and confidence levels, but for me i know from now on to bank on 2 hrs sim 1.5 hours actual flight exam time and possibly an hour or two's worth of ground instruction reminding you how to plan things. at the end i had an ir and me rating valid for another year all for the joyous cost of around £600 ish pounds (or the price of a nice 10 day half-board holiday in the carribean i later found out)