Thread:LOLisLeagueOfLegends/@comment-11200708-20180803150421/@comment-11200708-20180828100351

did you check the description

the description tells you that the maximum duration is 8 seconds at rank 1 and 10 seconds at rank 5

simple math

5 + x = 8 x = 3

7 + x = 10 x = 3