Is it possible to be a pilot for both the RAF and a Commercial company?
Basic officer training in the RAF takes 30 weeks, so you're already over your six months, even before you start pilot training. 

When you sign up you enlist for a minimum period which varies according to your speciality. Six to twelve years is typical.
Source

Assuming you get through pilot training and make it to a squadron, you're not going to just sit around and wait for a war. There's ongoing training, exercises, active deployments and other duties that will take up your time. Whilst there will be periods where your working life will be 9-to-5, there will also be periods where you'll be working nights, weekends, public holidays, and away from home.

I don't know what the RAF policy on second jobs is, but for practical reasons I can't see that you would be able to drive buses for easyJet or the like.