As noted, domestically max connection is 4 hours unless otherwise specified in Stopover section of fare rules. AS fares to/from Alaska actually allow up to 24 hours before stopover occurs. If connection is over stopover limit, you can still book it on one ticket (using multi-city), but it will just price each segment on a separate fare unless the fare allows for stopovers. AS US48 fares do not allow stopovers, but US48 to Alaska/Hawaii do (there is a fee for Hawaii stopovers). This is also specified in stopover section of fare rules. From US48-Hawaii fare rules below.



Note that just because a connection time between flights is less than 4 hours doesn't necessarily mean you purchase them on a single fare. There still have to be fare filings that allow the particular routing in their routing rules and married segment inventory availability to purchase on one fare. Otherwise, you'll just need to purchase segments as separate fares on one ticket using multi-city search.