^ Yup, that's basically what it means. It also means that, if you decide to not do 4 in the first 12 hours, that four will carry on to the next 12 hour cycle. For example:

0 - 12 hours = 4 leves added.
You have 4 leve allowance.
You do 4 leves.
You have 0 leve allowance.

12 - 24 hours = 4 leves added.
You have 4 leve allowance.
You do 3 leves.
You have 1 leve allowance remaining.

24 - 36 hours = 4 leves added.
You have 5 leve allowance.
You do 0 leves.
You have 5 leve allowance remaining.

36 - 48 hours = 4 leves added.
You have 9 leve allowance.
You do 8 leves.
You have 1 leve allowance remaining.

........

This is a hypothetical situation only, so not perfect, but I presume that's what it will be. Also, it's not hours of how much you are online, but in terms of earth hours.