We did a split stay last month were we stayed at the Poly Tower, went to Universal for 2 nights/3 days then went to BCV. We didn't want to carry all of our luggage to Universal so we asked someone with a tablet in the tower foyer if we could leave it. The first person we spoke to seemed quite new and didn't know but said there might be an issue with liability. They called a colleague over who said they definitely hold luggage for people on Disney cruises but they didn't know for other non-Disney stays so they contacted a supervisor. Thankfully the supervisor said it was absolutely no problem.
When we spoke to Bell Services the next morning they were very familiar with this. They just wrote our check in date for BCV on the tag along with LTS (long term storage).
I don't know the maximum length of time they will hold it, but they didn't have an issue with doing it for a few days.
