Unless this is a ‘bespoke’ provision (something like a mother and baby unit or other supported scheme???) where there is a likely gap between placements, this would seem excessive. (If this is a direct provision for the LA’s homelessness requirements I would seek your Housing team’s input.)
I would also be looking at whether the rent includes a void rate.
While it is potentially unreasonable on the person/claimant (I would expect homeless placements to be a daily liability or maybe a weekly one with no further notice period), it is also important to remember that a notice period cannot be enforced if the property is re-let – operationally, therefore, a longer notice period should not be necessary as the priority should surely be to get someone else in as soon as possible. (This is true of all tenure types – if the property is let to someone else, it brings an early end to any notice period.)
