On day one at Cranebank you will get a training manual which lists a whole series of hours/experience tables which show when you'll be able to start 76 flying and then ETOPS flying.
But in reality its all rubbish. The Christmas before last they ran out of ETOP qualified FO's. It cost the company a fortune as thay had to pay expensive overtime rates to cover the trips while a third of the fleet were tucking into mince pies at home. Suddenly we all got ETOPs courses.
I think now (and don't quote me) you finish your line training and then do 20 sectors before your rostered a 76 trip (shorthaul). From memory its then about 2/3 months before your ETOPS training which has to be a transatlantic trip.
Enjoy