What if the timing problem isn't always about the clock? How the hair reacts and the client's goal can change the outcome too. Sticking only to a schedule might not address the real issue.
Good point from @parkerr48. Hair type and what the client wants should guide timing more than a set schedule. Sometimes the hair needs more or less time based on how it reacts, so a fixed timeline might not give the best results.
People forget the room itself changes things. Air flow, humidity, even how warm it is can speed up or slow down a process. A set time in a damp bathroom is different than a dry, airy salon. The environment is a silent factor that messes with any fixed schedule.