On weekends, the Q53 is less predictable than the A on paper, but with a beach chair the bus can absolutely win if you time the stop right. The back-door boarding on SBS requires a paper ticket from the sidewalk machine before you board if you're entering at the rear. If the machine is down, board at the front and the operator usually waves you through or asks you to tap when it resets. They do occasionally check receipts, but not as often as people think.
One thing worth correcting: Woodside doesn’t have the A directly. If you're starting near Roosevelt/74th, a train option would be the 7 to Times Square and then the A down to Broad Channel, or LIRR to Penn and then the A. That’s two seats either way, plus stairs at the transfer points. With a chair and cooler, that changes the math.
When I did Q53 on a late-summer Sunday, I waited around 20 minutes at Woodside. Once onboard, the ride was roughly an hour and change to Beach 116th. The same trip by train felt about the same time but with more walking and platform time. Sunday morning before beach traffic loads up is definitely the window. After noon, both the bus and the Cross Bay bridge can bunch up.