A request becomes more considerate when it leaves time for another arrangement if the answer is no.

Short notice does something a request should not do: it turns a favour into a rescue. If your plan collapses when the person declines, then declining costs them your problem, and the decision is no longer really free. Time is what keeps a yes voluntary.

Ask earlier than feels necessary, and say plainly what you will do if the answer is no. Having an alternative ready is not a lack of faith in them, it is the thing that makes their choice genuinely theirs.