Welcome to Flyertalk and welcome to the BA forum.
The 11:55 was the first flight of today to BHD, thanks to an earlier cancellation some weeks ago and a weather cancellation of 09:30 service. Consequently the now delayed 11:55 is totally full and probably has been since yesterday.
That weather cancellation is affecting connections so I would say that the loads on these flights will be shifting from minute to minute. As things stand the first service with availability is the 18:15 and your 13:15 is now full. It closes shortly but it's possible that space will open up and then fill up in the remaining minutes. To get on the 11:55 then being at the desk at 10:55 is probably on the edge anyway, 10:50 would be better even though the deadline is 60 minutes.