Low Pressure

Part of me wonders if we can flip the script on the Iran situation and keep a low-level pressure on the Iranian regime until they begin to crack or need to negotiate. They think they can keep the low-level on pressure on the US until we cut and run. Why can't we flip it around? I don't understand why we always do this timetable thing with our adversaries - it basically signals to them: just hold out for 2 weeks. Which is easy to do. But if the timeline becomes uncertain for them, I feel the calculus changes.