Can you get a subdivision plat approved before the seller closes, or does the county treat the applicant's ownership as a condition?
Some counties will accept a pre-closing application from a buyer under contract, treating the equitable interest as sufficient to move through review. Others require fee-simple title in the applicant's name before they will open the file, which means you cannot start the clock on a six-month review period until after you own the land. The practical difference is whether you can trim four to six months off your hold by running entitlement and closing in parallel, or whether you are paying carrying costs on a parcel you cannot yet subdivide. What makes this harder to find out than it should be is that the answer often lives in administrative policy, not in the subdivision ordinance itself, so calling the planning counter and asking for the written policy is faster than reading the code. Have you confirmed which rule applies in the county you are working, and did you get that in writing?