Acceptable Period for Vacant Lot Due Diligence?

[Todd Nolan]

I recently subdivided a property and put one of the lots up for sale. I received an offer today but the buyer wants a 60 day due diligence period. Considering the lot was just subdivided by the municipality into a R-1AA lot should I give them the 60 days? The lots are cleared and graded (were part of an existing single family parcel). The lot is on a corner so the setbacks are a little harder to evaluate but I was thinking I should counter to at least 45 days. 

I appreciate any feedback. 

Todd