I did it in 2 weeks, and found it challenging and tiring. I would suggest 1 week would be very tough.
I would agree that 25 hours may be a more appropriate target to adequately fit in all the elements of the course. I did mine in 15, and my way round it was by using MFS 2002 as a pre training tool. I did 10 hours IFR on MFS 2002, while following the key bits in Thom. I can honestly say that I was perfectly ready to handle the basic stuff like the instrument scan, and even the more advanced stuff like the partial panel, with minimum time in the air.
This allowed for quality time to practice holds and approaches.