If you are looking to get it done quicker, Winter is the slow season in this industry and typically the time where the back log of work is lightest.
If you are looking to get it done before it costs you more $ (continuing damage), then right away is the answer.
If your work needs to be done on the exterior, Spring/Summer/Fall are the seasons you will need to schedule the work.
Typically, the sooner you have us out, the better. Sinking Foundations and Flooding Basements only get worse over time, cause more damage, and cost more to fix as the problem gets worse.