Hesitant to Marry – Yes
I suppose if you are caught completely off guard - you have never thought about marriage with this partner, have never discussed it with him or her, and have never been asked about it - then it might be reasonable to reply with, "I'm going to need a little time." But these answers most likely mean "I'm not sure" which translate into "I don't think I want to marry you."
Most proposals are not spur-of-the-moment and are not unexpected. Chances are high that you know how you feel about your partner, and you know it is coming, and even if you have never spoken to your partner about marriage specifically, the thought has probably entered your mind. If one person opens him- or herself to such an extent as to propose, you should respect that with an honest answer. Nothing is worse than stringing someone along with that false sliver of hope.
I have been dating my girlfriend for only a little over a year and we have already talked about long-term issues. We both make sure to clearly state that just because we're talking about it doesn't mean we can't discuss our future plans - individual and otherwise. It is important to know where you both plan to be and if you see yourself with your partner or not. Otherwise it's not worth the waste of time and energy that a relationship takes.
If you haven't done this, that's a problem. Of course it depends on the person, the people in the relationship - there are always exceptions to the rule. But even if the proposal is unexpected, I still believe the couple has discussed marriage in some way. Otherwise the person doing the proposing has developed a completely insane perspective of the relationship and needs to see a psychologist to discuss why he or she developed those fabrications.
So to answer the question, yes, the proposal's answer should come immediately because there should be no games in a relationship. If the person answering is genuinely hesitant with an answer, a few things need to be looked at: is it too soon for marriage or should you just cut your losses and move on? Of course, it's more complicated than that, but this answer is going to seem harsh when put in the most general terms. There has to be some reason for hesitation. Is it money? Is it security? Be honest to yourself and your partner - if there is hesitation, there is a problem that needs to be addressed. A hesitation might not be a no, but a person shouldn't need to be convinced to get married.
