The desk at BLT is only 1 or 2 CM's so there isn't a separate line for online. With online check in your room may be pre-assigned and your packet ready when you get there.
We did online check in for BLT last week. As mentioned there isn't a separate line for online check in but our packet as ready to go when we arrived. It didn't really matter though we were the only ones checking in at that time. It was about 9:30 am.
We're here now and did online checkin, with estimated arrival time of 12 noon. We actually got here at 12:30 and our FANTASTIC dedicated 2 BR was ready. I'd like to think that this was because I'd indicated when we were planning to arrive, but who knows. Our only request was an upper floor, so that may have helped, too.
It wasn't busy at that time, so there was no wait. 3 CMs were checking in most of the past week, plus at least one other person outside who seemed to be greeting and directing traffic.
I'd forgotten how small the lobby is ---- just a few chairs. At times we saw several families waiting in the lobby, but never saw a huge # of people. Our friends left on Fri afternoon and DH and I moved to a 1 BR. It wasn't ready before 11 and we were faced with storing luggage and us all being "homeless" for an hour that we had to kill before taking our friends to the airport. There was no comfortable place to wait at BLT --- other DVC properties have a lounge somewhere in the building, but BLT doesn't (that we're aware of). We were going to go to the Contemporary, but at 11:10 I got the text that our 1 BR was ready, so we all had a place to relax before the airport run.
We did online check in when we arrived last Saturday. There were a couple of people ahead of us checking in. Our room was ready when we got there at 10:30 and we got our room request (high floor). Probably not because of online check in, but who knows because we did say we would be there around 10am. Plus with everything in the packet all ready, it made checking in super easy!