When the property service contract expires, how long should the owners' committee inform the owners in advance?

You can notify the property three months in advance, which has nothing to do with the expiration of the contract. As long as the owners' meeting is established, the owners' meeting has the right to decide whether the property company will stay or not. If the property management company is told by the owner to leave his job and chooses a new property through bidding, the property management committee will terminate the property service contract after it is signed with the new property and takes effect, regardless of whether it has a term.