How long an appraisal takes depends on the type of appraisal and the individual schedule of the appraiser. VA appraisals seem to take the longest to schedule. FHA appraisals sometimes take a few days, but can be done the next day by some appraisers.
Normally, appraisals are sent into underwriting for the final approval of the loan. So, when the appraisal is issued, it may take a couple of days to get the documents out of underwriting and to the title company.
Bruce is right. You should have enough time to get everything done, but checking on the lender would be in your interest. Have your listing agent ask the buyer's agent or lender when the appraiser is scheduled to go out and when they expect documents to be at the title company.