How long would a Bitcoin quantum security upgrade take?

I've been reading about the possible quantum risks to Bitcoin, and one thing I'm wondering about is how long an upgrade would actually take.

Even if developers agreed on a solution, implementing it across the network would be another challenge.

New cryptographic signatures would need proper testing, wallets and hardware devices would need updates, and exchanges would have to make sure everything works before supporting the changes.

There's also Bitcoin's decentralized nature. No single person or organization can simply decide when everyone should upgrade, so reaching agreement could take time.

I know quantum computers aren't currently capable of breaking Bitcoin's signatures, but preparing for that possibility seems like something worth discussing now.

Could Bitcoin realistically complete a transition like this within a few years, or would the coordination and testing take much longer?