Hey Steve,
It really depends how motivated you are. Once or twice a week is pretty full time anyway. I would reccomend to get the IREX out of the way before you start, it can be easily self studied. Also it gives you some pretty good information that you can apply once you start the flying phase. I did all the initial sims once I got my PPL, and even a couple of flights. Then nothing for 2 years then completed my MEIR after my CPL, only needed one sim for the instructor to check my competency. I found I didnt really forget much its just a matter of getting your scan back up to speed, having said that I was 5 years from start to CPL MEIR so I was used to part time flying! ^^ gl with it anyway!