I see a similar variation. This is almost purely statistics. You complete a work unit, but getting credit depends on other people returning theirs. In my case most results are credited within 3 1/2 days but some have taken 2 weeks.

In a large team, the day to day variation is less percentage wise because some members will have an up day to counter others who have a down day.

There is also a fairly strong week day vrs. weekend modulation on points, results and CPU time. This is why Tuesday tends to be the day with the largest number of points credited.