When we were there in June it was just about empty around 5 - 6 pm. Never tried early to mid afternoon so can't comment. Dinner time was perfect! We practically had it to ourselves!
We were there the last week of July and there were no beds left late morning to late afternoon. Some people had put towels on them though and not around until a few hours later. We found if we got there about 10.30am we could find a bed or two for us to use.
We were there 2 years ago Easter and twice we tried to go to the pool around 2pmish and it was packed. We just headed over to CR pool....plenty of room and 2 pools. We did use the Blt in the evening with no problem and one morning
I have never had a problem with getting a chair at BLT in September. You will find that people leave towels on their chairs even when they are finished (rude!) or to reserve for later, but if there is no personal effects then grab a pool cm and have them remove the towels.
We were there the first week of September and it was never full, but lots of people did leave towels on the chairs after they were done so it was hard to judge. Most of the time we got chairs back by the splash area without a problem.
We found the CR pool better though, simply because of the sight lines. At the BLT pool I couldn't see my son at times if we had chairs back by the splash area. The CR pool is wide open and we don't have to spend hours upon hours in the water with him.
We just got back a few days ago from BLT. We went to the pool tons and there were always more empty chairs than filled ones. The tables w/umbrellas were harder to get. We stayed at a mod resort for our first few nights and chairs were almost impossible to get there. But BLT was awesome!