When I make an offer, if it's not accepted immediately, we will set a mutually agreeable deadline. I would not be concerned if it was up to one week that the candidate needed to decide. Beyond that, I would not wait, even for Mary Poppins…
If you didn't set a date, that makes it pretty awkward now. If I didn't hear within 4 business days, I would contact and ask for a decision or to know when one would be expected. Again, I wouldn't go beyond 7 calendar days from the first offer.