Afriad you're out of luck. But if you're inbound from BCN as I believe your profile indicates, you'll probably spend an hour getting your luggage, and then hike over to... T5 or T4? Either... you'll spend an hour on the bus, just about ready to spend an hour waiting for checkin to open, and then, the lounge will open... depends where you are heading for, but the BA T5 lounges will open early if you are on an overnight T5 lounges and most vitally champers is there around the clock.

Having said that, I wouldn't recomend it: you'll feel a bit lousy after a night awake: if you can grab 3 hours in the Yotel horizontal, it is worth it.

Just let us know where you are heading from and to.