lost spearman's text read

after you play lost spearman from your hand, any opponent may kneel 1 influence to return him to your hand.

Can my opponent only pay the influence and return him to my hand right after i play it, or at any point throughout the game pay the influence to return it to my hand?

thanks

Think about Old Red Priest, who reads "After Old Red Priest is killed, choose and kneel a standing location you control, if able." Can you wait to kneel the location for a round or two?

Or how about CS-Barristan Selmy, who reads "After Ser Barristan Selmy enters play, all players shuffle their discard piles back into their decks." Do discard piles effectively go away because all players just continue to shuffle them back into their decks anytime after he hits the table?

I don't point these examples out to be a schmuck. I am using them to illustrate the point that the timing structure of this game is very specific about "after X happens." Such effects only activate in the same timing window in which the card was actually played (or X actually happens). Beyond that, the activating occurrence is considered too remote.

So with Lost Spearman, people either choose to kneel the influence when he hits the table, or they deal with him.