Although my definition of a week does not say that the parts of the week must be days, habit makes us think so. The 8 parts of the moon calendar in Mamari cannot be true weeks - for the number of the nights seem to be unequal. But 15 nights in the first 4 parts and 15 in the second,  implies that we could (with my definition) regard half a month as a week. I.e., a fortnight can be regarded as a 'week' of the month.

1	2
2	6
3	3
4	4
5	5
6	3
7	5
8	2