You need at least a few months experience riding a 125 before you consider a direct access course.
Sorry mate, but I disagree.
There are literally hundreds of people who do the CBT and DAS all in 1 week.
With no experience whatsoever? I dread to think how competent they will be on the road.
I disagree too. Thought I didn't do my DAS over a week I did it over a month.
CBT then a 2 week break. (Theory done in this time)
4 more hours on a 125, 1 week break,
4 hours on a 500, 1 week break,
Mod 1, 1 week break
Mod 2, 1 week break.
I did all my training at weekends, other than my Mod 2 training/test as these had to be mid week.
Everybody learns at different speeds. If you've some experience driving a car ( I had 5 years, accident free) you will know how the roads work pretty well. If you're new to the roads I'd juggest spending much more time on them so you've one less thing to worry about.
I had 2 extra sessions, 4 hours each as I wanted more time to learn how bikes handle and respond and also build up some confidence and it was well worth it.
I hadn't ridden before at all and just after a month later I've my full license and a ZX6R to take out at the weekends.
Just be careful and sensible.
Good luck
Edit: don't even consider which bike you want yet as I guarentee you learning to ride will make you rethink it! it's that same horrible feeling as learning to drive feeling like you have very little control
