High-strength steels are the most susceptible. Specifications typically require baking for steel parts above a defined hardness or tensile strength threshold. Your drawing or governing specification will state whether relief is required.
As soon as practical, and always within the window the specification sets. The longer hydrogen remains in the part, the harder it is to remove, and any cracking that begins before the bake cannot be reversed.
Baking greatly reduces the risk but cannot guarantee it is gone. That is why critical applications pair baking with controlled processing and, where required, embrittlement testing.