I am not sure what the common practice is.
But I would not sign a contract to buy without a closing date and without a clause setting out the penalties if the other side is late in closing the deal.
If you sign a blank contract, there is nothing to stop them deferring the date for 12 months. Presumably you must do something about your current accommodation?
Call the seller and speak to them directly. Be flexible with them. They are probably trying to buy somewhere else. Put in a date three months from now and if everything goes well, you can agree to close earlier.
Brendan