Most hosts are available to let you store as long as you need the storage space! Unless the host communicates a specific time frame that their space if available, you can basically store your belongings with them for as long as you need.
If a host needs to end a reservation, they are required to give you 30 days notice. If there are extreme circumstances and a host needs their space unoccupied in less than 30 days, Neighbor will assist in helping you find an alternate storage space.
Pro tip: When you are filling out the reservation request, specify your estimated length of the storage reservation. This way the host will know the details of how long you intend to store before they approve your reservation.