It's been 2 weeks or so since my last mix. There was a mix that went down last week, I just wasn't one of the participants. In saying that most of my UTXO's have at least 2 mixes with some at 3 and 4 respectively.
By the nature of th protocol you instantly mix once you enter into the whirlpool. The idling in between is the waiting of a new entrant to provide new entropy to the pool, which will trigger another cycle.
Hope that helps!