I used the word "reserved" intentionally because my read of earlier comments indicated that if your butt isn't in the lounger - some would strictly interpret it to say you're technically reserving it, whether it be to go to the bathroom, fill your drink, jump in the pool, ride the aquaduck, whatever. So the question is - what constitutes "reserved"? Our definitions likely differ. So who decides that 5 minutes is OK, but 30 isn't? If someone isn't there you can't know why they're gone (drink, bathroom, pool, still in the room) - so you can't use that for your rule on when you move things.
Btw, I recently stayed at VB which is probably worse when it comes to reserving tables/unbrellas. By 9:00 every table/unbrella had stuff at it. Maybe half (probably less) had one person sitting at the table squatting rights. The others had the bag, clothes, etc. And no one was in the pool at that time - so I know it wasn't someone there. However - it didn't impact my trip. I just saw my stuff down elsewhere for the day.