My guess is 18 minutes.  
It would be really interesting to know if his passivity against the Heat was really due to being out of shape, or more a "between the ears" thing like Brandon eluded to; if the latter then it would be cool to see Chandler play physical with him and piss him off, propelling him to a breakout performance ... alas, I think it's probably the former and we're more likely to see something in the neighborhood of 4 points, 4 boards and a block or two.