At the club where I fly, you book the (freelance) instructors in two-hour blocks, regardless of whether you do groundschool, flying, briefings or whatever, and you book the aircraft, yourself, separately. It's up to you (with a little help from the instructor) to make the most of those two hours. If you make sure the plane is preflighted, fueled up and ready to go, with a flight plan submitted on the top of the hour, you can squeeze in an hour and a half of flight time into that two hour block easily. If you need the instructor to hold your hand while checking the plane and submitting the flightplan, you're going to fly less than an hour total.
It's quite common for instructors to have two two-hours blocks booked in the morning, half an hour lunch break, and then another two two-hour blocks in the afternoon. If you are further along in your training and need a three-hour block or a full day (for a X-C for instance) then that's negotiable anyway under the same conditions. Same if you only need a one-hour block for half-an-hour checkout on a new plane.
Strange as this may sound, but I think it's a fair system. The instructor gets paid for his time, regardless of whether he's flying, briefing or doing ground school. And this way you know there is time for a proper briefing - after all, you paid for it.
And obviously instructors all around the globe will generally set their prices so that at the end of a days flying+briefing, they take home a decent paycheck. If they only get paid for the flying hours and the briefings hours are for free, well, then the flying hours are going to be more expensive.