It depends what kind of program you participate in. If its not an "intensive program" then look for 2-3 hours a day. Once you get started you should usually know what you are gong to work on during the lesson ie turns around a point, pilotage, flight planning.
you should have read the text book prior to arriving at the flight school.
When you arrive you may sit down with the CFI for 15 to 30 minutes and review what you read and what the CFI will teach you that day.
Check the Weather, Notams, and for any restrictions such as TFRs essentially get a breifing for your area and time of flight.
Go out and preflight the plane. In the beginning you will do this with your CFI after a short while you should be able to do this on your own.
Then go fly with the CFI for an hour to 1.5 hours +/-
Land and sit down with the CFI to review the days lesson what you did well and what you need to work on then get a short breif on what you need to study next.
After your lesson its always good to hang around the airport and absorb the culture
This is just an approximation. Every school and independant CFIs may do things differently.