Not at all.
The only documents that are required are
- Mutual Non-Disclosure Agreement - which is for your protection against sharing of personal information and /or trade secrets.
- Engagement Agreement(s) - a document which outlines each party's responsibilities and lays out the pricing structure.
Neither document sets a time limit on the length of time we have to be in business together. All that is required is 30 days notice prior to the engagement being ended by either party for any reason.