I think the range depends on how interested you are in this agent and how interested you are in the other agents who have not yet made an offer. When mine offered, I gave the others a week. Then I realized after talking to the dude who is now my agent, nothing any of the others said would have made a difference. After 3 days I notified them all that I was taking the offer.
I just died a little inside. PLEASE, guys, do NOT do this. If you notify us you have an offer it gets bumped up to the top of the list, and it's highly likely in those three days we've spent time reading. For you to turn around AFTER you told us we had a week and then be like, nevermind!... ahhh, just please, think it through and if you must withdraw, do so, but try to avoid the above. i dont mean that to ream you, btw, hopefully no one wasted any time and all is good in the world, I just didn't want others reading that and following suit.
Also, to the OP a week is very much standard, and it helps big time if there is a weekend there (which obvs there is, if you do a full 7 days.). 90% of folks say a week.