The min hours for the IMCR is 15. I doubt most people can do a USEFUL set in that time though. To actually use it, you probably won't need to do the NDB/VOR holds (which the training is full of) but you will need to be able to accurately navigate IFR (which in practice means GPS/VOR/DME) and do instrument approaches including an ILS. There is also a lot of discipline to pick up, altimeter QNH/QFE settings etc. I would allow at least 25 hours - not easy to do in a week unless you have great mental and physical stamina.