“Max Sweeping Duration” refers to how long you can channel sweeping.
“Magic Circle Duration” refers to how long sweeping AoE stays in ground, which provides +1 skill level to all ground-skills placed on it.
This means, if you use Sweeping lv 1, then use Ausrine on the sweeped ground right after (within 6 seconds), you’ll get +1 lvl for Ausrine for whole Ausrine duration.

, you can just click the seeping without channeling for his full effect ? i read this somewhere
perma free rank resets when