Can unstable angina last for 24 hours?

Don't wait: In unstable angina, you are at high risk of losing heart tissue causing loss of muscle and/or rhythm disturbance ("arrest") leading to sudden death or permanent disability. It is unlikely you would have continuous unstable angina pain for 24 hours; more likely to have on-off pain over the 24 hours. That said, seconds and minutes count – don't wait!

Yes: by definition unstable angina is a change in the frequency and character of a previously stable chest pain .Thus a chest pain previously infrequent and usually brought by moderate exertion now comes at rest and frequently,lasting longer etc. it can start slowly but progressively and may go on for days before the next stage which is a heart attack

Yes: In unstable angina the biochemical markers of myocardial damage and necrosis(cell death) are not present. One cause is a sudden rupture or crack in a silent atherosclerotic plaque causing blood clots(thrombi) to form which can enlarge to block the artery or can break off and embolize. Patients with 24 hours of chest pain require emergency cardiac catheterization and angioplasty or surgery.