There used to be a difference between the item types, but it’s been the same across all 3 for about 6 months now.
Lesson
4 hours
8 hours
1 day
2 days (complete this and you are at guru)
1 week
2 weeks
1 month
4 months
For any times 1 day or longer, subtract one hour. Additionally, these times are calculated from the previous hour. i.e. you do a lesson at 6:30, it rolls back to 6:00 for the calculation and then the review comes at 10:00.