This kind of operational breakage very often results in expensive engine damage, due to fast-moving pistons in the engine block impacting valves which may be open. Some engines are of the freewheeling type , that is, due to their cylinder head design, valves and pistons are very unlikely to collide, therefore no damage will occur. Replacing a timing belt will take between 2.5 to 5.5 hours, depending on how easy it is to make the change, given the limited under-hood space in many of today's cramped engine compartments. We recommend that front engine seals also be replaced along with the belt. Oil seals are inexpensive and will leak eventually if not replaced with the belt.
Some models also recommend water pump replacement at the same interval.
If you drive until the belt breaks, you could be facing anything from a cylinder head overhaul to a major engine rebuild. Engine timing belt replacement is a required maintenance job on a growing number of engines today. If it's with a timing belt, get to know the car maker's recommended replacement interval.