The main contract points at financing; the 40-11 holds the actual exit.
Buyer Approval — the lender approves the borrower (income, assets, credit). The buyer may terminate within the stated number of days after the Effective Date by giving notice plus the lender's written statement. Miss the window and the contract is no longer subject to Buyer Approval.
Property Approval — the lender approves the collateral (appraisal, insurability). This one runs all the way to 3 days before closing.
The 40-11's ¶2 says it plainly: strict compliance required. The Buyer Approval window does not stretch for weekends.