What is a Bussiness day per Ohio state law?

I've signed a contract to have a wooden deck built on 05/17/2007 (thursday) and paid a deposit in the amount of $720.00. Due to some unprecedented circumstances, I have cancelled the contract by hand delivering a written notice on 5/22/2007 (Tuesday) but the contracter is disputing that cancellation is not in compliance with the buyers right to cancel and is not willing to refund the deposit. Buyers right to cancel as written on contract states "Buyer may choose to cancel this contract by dellivering written notice to the seller at any time prior to midnight of the third business day after the date written above." Even though contract does not specify sellers business hours, contractor claims that they are open on saturday 9:00 am thru 3:00 pm, sunday 12:00 am thru 3:00pm and monday thru friday available only by appointment and is implying that the weekend days are also considered as business days per state law in Ohio. Does it mean I should have cancelled by sunday (05/20/2007) to get my deposit back?

"Business day" means a day of the week excluding Saturday, Sunday, and a legal holiday as defined under section 1.14 of the Revised Code.

one definition above!!