Being in WAG territory, this is probably due to a manning issue. There are a number of things at play here. As mentioned upthread, the staff are a contract service company and dress as BA for the duty. They also dress for other duties in different rigs and move around! They are probably setting it at two hours as that is when the check-in desks open. That will be when the "BA dressed" people come on duty - possibly having changed from a different rig. The lounge caterers are a different contracted firm.

That people with no checked baggage can get airside on a printed BP or app ahead of that time is possible - but also relatively unusual for the majority of travellers at BHD. Why might a traveller be there for more than 2 hrs? Because work finishes early etc and hanging around in a comfortable lounge with food, drink and internet etc is a convenient option.

I had noticed that the lounge was shut at one point recently and was surprised, but thought no more of it as I was on a FlyBe jaunt. Now I can see what is going on. Whilst many flights are about 2 hrs apart there are some longer gaps and probably a cost saving can be made by closing the lounge for an hour or so for both firms. It is probably rare for more than one or two people to be there for over two hours so they have probably made a financial call.

When the EI integration starts it will be reshuffled anyway as they use the other lounge at the moment I think.

I am in BHD next week and will ask questions (if I remember).