Mike, a property owner, is in negotiations with Oscar, who manages Lawn Lover's Lawn Service, over a 12 month lawn care contract. Mike sends the following email to Oscar: "Hi Oscar, I'd like see if I could get you to take of all the lawn care for my property at 123 Fake St for the next calendar year. This would constitute a twice monthly service on your part, and the service would include mowing, pruning as needed, weedeating, trimming bushes, and removal of dead leaves and other lawn debris. The total price under the agreement would be $8,000, payable in four quarterly installments of $2,000. Please let me know if you accept my offer within 10 days. Thanks. Mike November."

Three days later, though, Mike calls up Oscar and revokes his offer. Oscar says he can't do that and that Mike has to leave the offer open for the full ten days.

Does Mike have to keep the offer open for 10 days?

No. Mike can revoke the offer anytime he wants to, as long as Oscar hasn't accepted it. Here Oscar did not accept before the offer was revoked, so there is no more offer.

Yes. Since Mike basically told Oscar that Oscar had 10 days to accept his offer, Mike has to stick to his agreement. He can't just cut the time without telling Oscar. That's not a good business practice.