PJ is right... an hour of flight time does not take an hour. If you really think about how much time you need to carve out of your day, figure realistically carve the number of hours you want to fly, plus probably about 1 hour. For me, I need 30 minutes to get to and from the airport, and figure another 30 minutes to get the plane out, preflighted, refueled when you're done, put it back in the hangar, etc. And that isn't including the time you spend when you end up not being able to fly. A few weeks ago I had one day where I was actually at the runway ready for takeoff and then the winds picked up and went above what my sign-off allowed for (this was before I took my check ride), and so I had to turn around and go back to the hangar. So that was 45 minutes - 1 hour, and I didn't fly at all!
It is most efficient if you can schedule flying in after something (like if the airport is on the way home from work) or if you can schedule larger blocks of a couple hours, but depending on what you're doing, several hours of flight time can be really exhausting. The most I've done in one day was 6.5 hours (3.5 in back, 3 in left seat). The most I've done in one day period was 5.1 hours, all solo. In both cases at the end of those days I was fairly worn out, and those were just XC flights. If you're going up and actually doing a "hard" lesson, especially at the beginning, you can be tired after an hour. There was one time we were up for about 30 minutes and I managed to scare myself doing a departure stall and put the plane in a spin. After that, I was done for the day.