Hello!
The length of the lesson depends on the student and how much time they need. I prefer to teach online due to my busy schedule and also due to the convenience.

The way I teach my students is by first making them answer some questions to see how much content they already know. Then, I follow this by teaching them new content, allowing them to ask questions wherever necessary. Then, I ask the students to re-explain the key concepts to make sure they have understood them. Then we end the lesson by looking at past paper questions and how to tackle them. I like to focus the most on exam technique as this is often the most valuable to students. For example, if the lesson is one hour, 30 minutes will be content and the latter half will focus on exam questions.
I have an iPad that I use to draw any diagrams that may aid in explanation, and I make the lessons as interactive as possible.
The typical length of the lesson is ~60 minutes, however this is determined by the student.

I have been tutoring previously for a few years and my students have improved massively in their grades.