I’m the back-up buyer. When does my option period start?

A seller accepted my back-up offer on a home that’s currently under contract to another buyer. I paid for a 10-day option to terminate, but when do my 10 days start? I don’t know if I’ll even get the chance to purchase the house. You have the option to terminate at any time while you’re in the back-up position. The option period specified in Paragraph 23 of the contract-10 days, in your case-doesn’t start until your contract becomes the primary contract, which is the date you receive notice from the seller of the termination of the first contract.