If you take 5 cruises up to 24 days you will get 1 credit for each
I do not think my math is that bad
5 x 7 day cruises =35 days = Bronze
5 x 10 day cruises = 70 days = Bronze
5 x 20 day cruises = 100 days = Bronze
1 RTW cruise 180 days = Gold
All depends on how you work the numbers
Where are you seeing minimum number of days to get to the next level?