Hi Jasmine,
The best time to apply during the 3 month window depends if there are going to be any changes in Benefit entitlement which affect the amount of transitional protection. Changes could be fluctuations in income or children leaving the household etc. Also remember the timing of UC payments is different from Legacy Benefits and is paid monthly.
As far as Housing Benefit is concerned you are best advised to contact the Housing Association which should have a Financial Inclusion officer who could help you.
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems