Worst case, weeks.
When I bought my track car, it had a nasty CAS O-ring leak that had probably been there for a couple of years and the heater hose was just starting to swell from the oil bath. Oil soaked hoses swell before they let go, so just keep an eye on it. As long as the heater hose dimensions are unchanged and it feels pliable to a squeeze test, it still has plenty of strength.