Yes, it’s essentially for X [time] keep one backup every X [time]
With support for
s - second
m - minute
h - hour
D - day
W - week
M - month
Y - year
One “different” option isn’t really a time, it’s more of a concept
U:1D - for unlimited time keep one backup for every 1 day
1D:U - for 1 day keep unlimited backups
It’s also worth noting the time-frames are somewhat fuzzy, but they do not accumulate. So even though you keep one every 8 hours you don’t have to backup exactly at multiples of 8 (e.g. 8, 16, 24) to get 3 backups a day. But since they do not accumulate it means you could not have 3 backups within 1 hour even though they are the only 3 backups that day.
Might make sense to write a How To on this subject