Time to command used to be approx 2 to 3 years but that could possibly all change from now on. As mentioned the wet lease will delay promotions as will the over 60s now being allowed to stay on.
There is only one pilot thats been promoted in 6 months and he had over K6 hours and was a Captain in his previous airline. He was also prepared to go to MAN.
On the flip side you maybe lucky as people are likely to leave in droves next year. Keep your nose clean and don't fall foul of Jekyll and Hyde (TG & DW) and the rest of the corrupt incestuous training dept and you should be OK.
As Shaftspeare said there are much better and more secure options out there than GB.