A week??? I'd give people a day or two and then move on. I mean either they're going to be there and they want them, or not. They don't need a lot of time to decide while you wait around for an answer. Give them 24 hours or maybe 48 on the weekend to get to their computers, tops. For the next people I'd definitely put in the email, "Please let me know by XXX or I will contact the next person, thanks so much."