Interviewing in July - would start date necessarily be September? I applied for a position with the application deadline of April 30 and was contacted for an interview last week. My interview is in mid-July. Can they reasonably expect a candidate to start in September if they make a decision quickly? If so, would it be appropriate to ask for teaching release for the fall semester? Not sure if asking for a january 2016 start-date would be a deal-breaker from their perspective when they are moving so quickly. Thanks in advance. 

Edit: this is in Canada.
This may depend to some extent on hiring norms in your field/country.

I would assume that if they are interviewing people in July, it is because they really need someone to start teaching in the fall.  (Otherwise they would wait another year and hire for next fall, when there would be more candidates available; I would assume that by this time of year, many people are off the market.)  As such, I wouldn't think they'd be likely to go for a deferred start date, or a complete release from fall teaching.  A modest teaching reduction is conceivable; you may be able to tell during the interview whether this would seem to be in line with their needs (e.g. if there is one particular class that they really need someone to teach).  

The size of the department may also give some indication - a large department is more likely to have some flexibility than a small one.

You might be able to negotiate for classes that require less advance preparation (e.g. introductory courses instead of advanced).  You might also be able to get more money for relocation, on the grounds that you're moving on short notice.

But my gut feeling is that you should be prepared to show up and start teaching in September.