Based on today's market, put it on the market now.
You do not know when an offer will arrive.
It could sell tomorrow or 6 months from now. When the offer comes in be prepared to negotiate. Ultimately it would be far better to have your buyer in hand. If you cannot reach agreement on occupancy consider a double more.
If you new house is ready and you do not have a buyer can and are you able to close on the new house?