Hello! Not sure about your NPPL P1, but when I did my IMC in 2010 the rating training itself counted towards the 25 hours, so I only had ten hours to polish off after the IMC test (which I did by bashing out a trip to France, bien sur) before I could apply to the CAA to put the rating in my licence.
I guess my point is you don't have to do 25 hours before your start the IMC training! Hope that made sense.