Since you hold the ♥A as well as the ♥10, you know declarer has no guess and so you can, in fact, take your time.

Can you see the advantage in taking the ♥A at once? Partner's ♠8 looks like the top of a doubleton (or possibly a singleton). You want to play the ♠Q and a third round of spades while partner has a trump left. Declarer now has to overruff rather than discard a loser. This might beat the contract (as here) or save an overtrick, depending on the precise layout.