I was doing 2 flights a day of around 1 hour. And it still felt like I had too much time sat on the ground waiting!
This reminds of the valuable cliche "better to be sat on the ground wishing you were flying than up there and wishing you were on the ground."
Whenever a new student requested that they flew say 4 hours per day I would always agree to it but with the advice that they were likely to become overwhelmed quite quickly In the vast majority of cases this happened and the student would cut back to the recommended two flights per day. Of course, different phases of the course require different approaches. The general handling elements can easily become overwhelming when covered intensively. The navigation exercises at 3-4 hours per day is unlikely to be overwhelming.