I like equations. Simple math to keep me on track. For instance I check my to do list at least twice a day or water my plants once a week. Easy stuff like that. With that in mind, I created a equation or rule (and remember sometimes rules are meant to be broken) for how long one hair time session should last to keep it fun. That equation is:
Year of child x 6 minutes = Hair Time, Fun Time
The idea is to train your child to sit patiently for hair time and by the time they are 10 they hopefully can sit down straight for an hour long session and still enjoy themselves.
Because the time is shorter at first, you may have to do multiple sessions when they are young. Be sure to tell them that. Try using a timer and explain to them when it buzzes you are done. Use it to start hair session two; tell them that you will give them 10-30 minutes of their time before you have to finish their hair for another x amount of minutes. Breaks are encouraged during hair time even though it may prolong the session.
The goal is to make hair time a bounding experience so focus on the journey and the time you are spending with them.
How long does hair time last for you? And how old is your child?