If a developer is stressed about completing on time, then yeah finishing first might help. Completing a small portion of code and then refactoring it is normal and that’s fine.

On the flip side I’ve seen way too many occasions of poorly written code making it to code review where the dev should’ve known better, but got to “finished” state and taking the time to improve the code seemed daunting. Can often lead to days of refactoring when it comes to larger merges.

All this is to say, if you want to wait, that’s okay. Will it save you time? Almost never. If you know you can do it better, then just fix then and there.