Why would a buyer take their property off the market in the hope that you could come up with cash that you do not have in another two months? I would fully expect that there would be a request for an extension of the contingency at the end of those two months because you are oh-so-close to having the down payment. I may appear cynical to some, but I think I am being realistic.
Talk to your lender right away. If you are still saving up for the down payment have you considered closing costs, prepaids or reserves? Before you write an offer, make certain you have covered all the issues necessary to close.
Assuming you have these addressed and are 100% positive you'll have the down payment in 2 months, consider your request for a long closing a seller's concession. Seller's generally want to close in 30 days or less, depending on their situation. Sometimes, they are okay with a longer close, but they want a solid pre-approval letter, good earnest money and a strong offer.
Have your agent ask the seller's what type of terms they are open to. Sometimes a longer close is preferred as long as all other terms are strong.