By crack the rotation I mean that he has a more or less defined role. Pop has his designated starters and a clearly outlined second unit.
He may make game adjustments depending on match ups, but it's clear that TD and Tiago are his big man starters with Boris as the primary backup. He'll filter in SJax or Bonner depending on need. Blair gets what's left at garbage time.
Unless Pop breaks his pattern of the past decade, Baynes may get Blair's minutes (I'm assuming Blair will be traded if Baynes is brought up) for the rest of this season. It would be a huge break from Pop's history if Baynes sees the court during important minutes or this year's playoffs.
Reportedly, Baynes is signed for a few years. I'd have to guess that he'll make his first significant contributions at next season's training camp. Until then, I wouldn't be surprised to see him playing most of his time in Austin with the Toros.