Give a project unlimited time and it’ll take all of it and still not be done.

Without an end date, work expands to fill whatever is available, because there is always another improvement you could reasonably make. The absence of a limit removes the moment where you have to declare something finished, so that moment never arrives on its own. Past a certain point more time rarely produces a better result. It produces a longer middle.

Pick a date before you begin and treat it as fixed. Let the scope flex against it rather than the other way around, and release whatever the date finds.