The approved Part 147 Cat A course is 800 hours; a typical approved course is 859 hours, with 490 theory, 252 practical and 117 OJT (ie structured training OJT, not hanging about in a hangar). This particular course would be accomplished in 24 working weeks. The extra hours are to allow for student absence and sickness.
Work experience acquired while using an A licence could count towards the work experience requirement for a B licence, if it was relevant, but I'm not certain that an A licence holder has a reduced work experience requirement for a B licence.
It should be possible to gain 3 years work experience as an A licence holder while getting the Modules for the B Licence. The Practical requirements could be covered in the same period.
By definition the work experience required for a B licence is carried out before the licence can be issued, and experience gained as an A licence holder is going to be more useful, probably, than experienced gained as an unlicensed mechanic.
As you say, going for an A licence and then B is a good route for some.
Edit: The requirement for work experience, moving from A1 to B1.1, is 2 years. Doing the B1.1 from scratch would need longer (3 years) if you do not do the full approved 2-year course. So it is true to say that having an A1 licence reduces the work experience requirement for the B1.1 licence, except in the unlikely case that the A licence holder does a full-time 2-year course for the B1.1 licence, when 2 years experience are needed instead of 3.
Incidentally, an A Licence holder can miss a few sections of the Module 7 and Module 10 of the B1.1 Modules, so there's another (very) small advantage!
Last edited by Capot; 18th Feb 2010 at 19:59.