If you’re flying regularly then it is quite busy.
After a flight (and the hour or so debrief) you have notes to go over, maybe some chair flying or even work on an instrument trainer. Beforehand you’ll go over notes and brief yourself based on what the lesson plan is, as well as potentially draw up a PLOG, mark up charts, look at weather, read NOTAMS, run performance etc. You’ll also need to do general reading around of air law, the aircraft POH and the like as you integrate what you learned in ATPLs in a practical setting. You’ll then be briefed by your instructor. Normally the student will also pre flight the aeroplane, super keen students who get noticed for jobs and recommendations hang around and drag aircraft out of hangers etc. and maybe help out in ops.
There’s down time, but you don’t just rock up and fly for 90 minutes then go to the pub. A lot of students could save themselves a lot of money by learning stuff on the ground (flows, performance, affects of controls, systems, weather etc) rather than in the air when they’re paying an instructor. It is in the very dim and distant past for me now but we used to go and sit in one of the tech aircraft and chair fly circuits.
If and when you get to an airline, the first TR is like drinking from a firehose and getting into good study habits will pay dividends.
Learning how to break down a flight plan, NOTAMs, weather, MEL/tech issues is an invaluable skill that you will begin to hone during flight training.
Seen from your post history you are on the speedbird academy - congratulations, see you at Heathrow some day.