Concurring with @vonbrand, try to split the material "sideways", so that the subsequent hours do not depend on supposed (instantaneous) mastery of the first hour, etc.
I've taught summertime classes that met two hours a day, five days a week, instead of what would have been a single hour on MWF, for a full term. When I was young and foolish, I thought that in the upper-division courses of this sort it would be better, since there'd not be such gaps between episodes. But, in fact, exactly as the question anticipates, it was horrible. Not only is there the literal incapacity to adequately assimilate the first hour's material as prerequisite for the second... but there is another terrible problem, namely, few students are acquainted with such a pace and all it entails.
Thus, many students, perhaps a majority, can't help but use their usual "pace" even in doubly or triply speeded-up courses. This includes procrastination at the very beginning, typically, ... which, while unwise in ordinary circumstances, creates an impossible situation in speeded-up instances. Even the students' "catch-up" chops are woefully inadequate for a speeded-up situation, since they are usually not-so-good at catch-up even at normal speeds.
I suspect all-the-worse if you don't actually meet with the students every day, because many will misinterpret the "off-days" as days to not think about your course, etc.
In particular, I'd suggest nearly-oppressive amounts of homework to get their attention on the off-days, or they won't take you (the course) seriously. And, again, in your three hours, as you anticipate, it would be foolish to hope for immediate assimilation. As @vonbrand suggests, making things not too-intensely depend on each other is highly desirable. (Thus, the traditional "strict logical ordering" is infeasible.)
A very unfortunate and impractical pedagogical situation, for sure.