We usually do owner finance so I have little experience with this. 

Received an offer we would like to accept but appraisal contingency is for 24 days 

I really don’t want to tie the house up for that long if the appraisal comes back lower than selling price. Which I think it may as house prices have simply exploded in the past 3 months. 

Is 24 days too long to allow for an appraisal in your opinion?

Any other words of advice are appreciated.  Thank you 

An appraisal contingency is really not so different from a financing contingency if the buyer is getting a mortgage. They won't be able to get financing if the appraisal comes in too low, so they will have the option to terminate anyway during the 30, 45, 60 day mortgage contingency period, whatever it may be in your situation. 

Additionally, if these people's appraisal comes in low, so will every other buyer's. Sometimes it just is what it is and you'll have to negotiate the price closer to its market value. If it's an all cash deal and they don't have to wait for the lender to do the appraisal and they are doing it themselves, then make it closer to 14 days. if they are in control of the timeline, no reason they can't get someone out sooner. 

Ok great thank you!

I will request 14 days 

Thank you