If you cannot locate this on the offer, then ask your agent to assist you, assuming you have an agent representing you in the sale.
If a specific closing date is important than you, then you can counter that "time is of the essence." With this clause, if either party does not meet any dates in the contract, then the other party may cancel the contract.
Please speak with the agent representing you for more information. If you do not have an agent representing you, then speak to your real estate attorney.
If not, you want to see proof that the buyer can buy the house by seeing a pre approval letter. Once you have that, feel free to contact their lender and ask how long to close.
Hope this helps....Amanda