I'm presuming Tyler is Tyler, Texas. In Texas (and in most other states that have option periods) day 1 of your option period starts the day following the execution date of your contract. Regardless of when you signed your contract, the execution date could be that day or some subsequent day, depending on when the seller signed, and when you were both informed that the other party accepted the terms of the contract. Check the contract that was submitted to the Title company to see what date was written in as the execution date of the contract.
Presuming it was the 14th, then day 1 of your option period starts on the 15th. Simply count the days (calendar days) on your option period, and the end date occurs at 11:59pm on the last day of the option period. For example, if the execution date were the 14th, and the contract had a 10-day option period, then the option period should end at 11:59pm on the 24th.