If necessary, you can make an estimated tax payment at www.irs.gov/payments at any time you like. Just remember to print your receipt and store it with your 2020 tax information.
Understand that if you sell the rental property in the same tax year that the last renter moved out, then it makes no sense to convert the property to personal use. Leave it classified as a rental. All repair costs are deductible as a rental expense on the SCH E. Maintenence costs, depending on what they are would be claimed on SCH E as a maintenance cost, or reported as "carrying cost" if the cost was incurred for the sole purpose of maintaining it's sale value. But from what I've seen and experienced in the past, if you manage to sell the property within 4-6 months after the last renter moved out, practically all expenses incurred will be rental expenses claimed on SCH E, with a slim possibility of a few carrying costs which basically add to your cost basis.
One decent example of carrying costs would be property taxes paid at the closing (and not before) to cover the number of days you owned the property during the year, from the day after the last taxing period ended, up to the day of the sale closing.
