Wrongful dismissal case was settled prior to arbitration date. Paperwork signed nearly 3 weeks ago and told “check is in the mail” via registered mail. Nothing received and no tracking number given despite my requests. What are legal timeline/deadlines? Should interest accrue? What do I do now?

This would be a question for the lawyer who assisted you with the settlement. Hopefully a timeline was negotiated as a part of the terms of settlement, in which case the breach of the timeline would be a breach of settlement, which has legal remedies.

If your lawyer did not incorporate a timeline then all you can do unfortunately is continue to follow up.