It's an earnestly conceived idea, but not a good one in my opinion. Based on my experience, it's a solution in search of a problem.
I've handled thousands of orders on Fiverr, and it is not common that anyone requests a revision just to bide time while they get approval from a client, for example. But when they do so, I just write back graciously and give them a few days. If more than a day or two goes by, I politely prod them. If it stretches into many days, I re-deliver. Very seldom, if ever, has a client re-requested revision to stall further.
Seems to me the only way to make this equitable would be to provide an identical button for sellers. If buyers can extend approval time without the seller's permission, the same courtesy should be extended to sellers who want to extend order delivery time. Or, flip that over: For sellers, there's an option to appeal to the buyer for a time extension before delivering, but that is contingent on the buyer's ok. The buyer can refuse. If buyers want more time to approve a delivery, shouldn't they be subject to the same conditions?
Here's one other interesting possibility. Now don't laugh, but what about making it an extra? Standard approval time is three days. Let the seller set a value on additional approval days: $5 per additional day for time extension, for example. Let's say that 10% of buyers feel they may need more than three days for approval. And let's say that's $10 added to the order. It would mean a little bit more income for the seller (who should be compensated for their inconvenience), and it would mean a pretty enormous sum for Fiverr, with its hundreds of thousands of buyers.