The migration you'll wish you started in year one
Every codebase ends up with a migration the team avoids until it can't. The teams that did it early always wish they'd done it earlier still.
Somewhere in your codebase right now is a decision you regret — a framework version, a database choice, an auth model. Everyone agrees it should change. Nobody does it. Each year that passes makes the migration twice as expensive.
The economics get worse, not better
More code is built on the old foundation each quarter. More edge cases get added. More people depend on the current behavior. The day you finally do the migration, it'll be the largest project the team has ever shipped — and it's only getting larger.
Start the migration now
Don't wait for the perfect window. Don't wait for the quarter where nothing else is happening. The perfect window doesn't exist. The longer you wait, the worse the trade. Start small, parallel, and move incrementally.
The best time to start the migration was a year ago. The second best time is this week.