We did three intra-resort transfers (OKW to SSR; SSR to BWV; and BWV-std to BWV-preferred) this past January...at that time, all intra-resort luggage transfers were done between 1 and 3 (regardless of when you asked Bell Services to come get your luggage, or when you dropped it off, and even "just" changing rooms at BWV)...after 3, the new resort Bell Services delivers your luggage to your room, but you must be in your room to receive it...so we just called Bell Services when we arrived...once we had to wait 30 minutes; the other two times it was essentially immediate...
They do expect tips ("they say" $1-$2/bag, depending on how many bags--first two transfers it was just two of us, w/3 bags to transfer; I gave each bellhop $5; last one our party had grown and we had 10 bags to transfer (backpacks and grocery bags as well as suitcases)...I gave each of those bellhops $15)...
Getting to Downtown Disney by 9 a.m. is possible, but not "easy"...buses do start running by 9, but they seemed to be few & far between to DTD that early in the day (park buses, on the other hand, at that time of day are plentiful)...you might instead want to head to a park, and then take the SSR bus back to SSR after you're finished in the park you choose...
Cabs between the resorts aren't expensive, but I was surprised at how much they do cost...on our T-giving trip, I left SSR via cab to meet family staying at ASMu...it was $10! That did surprise me...but it is the most time-efficient way to move between resorts, particularly early in the a.m.
Split stays are pretty easy and painless so long as you don't lose sight of the fact that on your day of transfer you won't be able to get your luggage til after 3, and then only if you're in the room to receive it; and so long as you're prepared for tipping...I know by the time I finished with two tips per transfer after 3 transfers I felt like tipping was a significant expense! I spent about $50 on tips for our 3 transfers...and they're pretty insistent...I know on our last transfer, I wanted to save the cash so I sent my two 18-year-old boys down to the bellstand to retrieve our bags...the bellhops there at first wouldn't give the boys our bags, saying they'd bring them themselves...when the boys insisted, the bellhops walked back to our room with the boys...(I wasn't there and the boys said they went ahead and gave the bellhops their tips...I reimbursed the boys)...
Happy vacation!