I would say around 9 months would be about right if you work full time. I took 8 months from start to finish (with probably 6 months study), and this was fairly typical of the others that attended the same ground school as me.
Best thing is to make a loose plan and just see how it goes without putting too much pressure on yourself. I planned for 10 months in 3 sittings but ended up completing in 8 months with 2 sittings.
Good luck.