Architecture & practice·Estimation and planning
you agreed to spend two days on it and to come back with what you had, whatever that was.
Timebox
Fixing the time and letting the scope or the outcome vary. It is the standard control for open-ended work — investigations, spikes, debugging, proofs of concept — because such work has no natural end and will absorb whatever it is given. The discipline is the ending: a timebox that is silently extended twice was never a timebox, it was a wish.