Is there any minimum or maximum period of a tenancy agreement?

No.

The agreement should define a period of time called the 'fixed-term'. Generally, tenancy agreements have a fixed term of either 6 or 12 months but the parties can agree to have a tenancy agreement for any length of time.

When the fixed-term period ends the tenancy agreement does not end unless it is terminated by the tenant or the landlord. If it is not terminated, the agreement becomes a continuing agreement with the same terms and conditions.