I think by 'stacking' they meant proc-ing gears from a different hotbar items by mistake when you switch, since actual proc stacking was removed long ago. Example: you use a dmg set and cast a skill that has damage over time effects. Now if you switch to kraken set it will proc even if you don't want that.

It feels like the delay is 1s which seems reasonable to me, although I only use kraken procs not star beast procs, so I cannot argue about that.