Restarting German heavy-gun development in 1935

If Germany restarted 16.1-inch and 18-to-22-inch gun development in 1935, when could it have six usable weapons?

Probably around 1939-41, because Germany would be rebuilding the entire heavy-gun development and production system.

The delay comes from discontinuity, rather than barrel manufacture alone. Germany would need to recreate design expertise, tooling, proof capacity, and production after years without comparable work. A 16.1-inch weapon and an 18-to-22-inch railway gun would each place heavy demands on that rebuilt system. Even with serious resources from 1935, a small serviceable batch would arrive only around 1939 to 1941.