Mine (not BA) took about three months, but that was because we didn't have an in house system for this so went on detachment to Thomson. That meant all of their SEP, CRM, recurrent stuff before the technical bits which was something like 3 days tech, 3 sims inc a PC and then line trg, so 4 short (European) sectors then 4 NAT sectors to cover ETOPS/NAT/MNPS (now HLA). Once we brought it in house it was much shorter and limited by the availability of training sectors.
hth