Got caught out by this a fortnight ago. Arrived at T-4 hours thinking I'd drop bags and work in the lounge and was told 2.5 hours was the limit. Mentioned the lounge screen and was confidently told that wasn't a thing and never has been. Sat in Pret for 90 minutes and then went back to drop bags. Eventually got to lounge to see the All Day Check-In message on the screens...
Complained to BA and got a £50 voucher, which I suppose more than makes up for the 99p I spent on a Pret filter coffee!