Dear Square,
Aryeh Kaplan writes that his peers agreed to learn everything by heart. He says that it was very difficult, but very quickly became easier to do. It got to the point that they were able to memorize whatever they were learning in the same day.
When I was in yeshiva, I noticed that whenever someone learned the same topic consecutively, (For example, he switched yeshivos and was learning again what he learned the zman Bedford..) They basically knew it verbatim from any point that they picked up the discussion.
In sum, learning by heart is more about mental preparedness, than it is time consuming. If your motivated, than it is worth trying to fulfill it.