I would usually put in the additional clauses " The closing shall take place X amount of days from the effective date.
There is another option and that states: All the time periods under the contract shall commence from the effective date under the contract.That would mean that the date you have on the original contract would be the closing date.
Without anything in writing you really do not have executed contract.
Your agent should try to get the approval of the contract in writing.
Hope this helps.