The answer you seek really depends on which operator you are considering (or not).
A bidding/ preferential bidding system could offer anything over a 14 day period depending on the pilots taste, but would generally balance out to 'company average' over a 28 day (or calander month) period. (legacy US carriers/ BA etc)
An allocated roster system (possibly with preference weighting) would give a fair indication of lifestyle over a 2 week block. (Cathay Pacific, VS etc)
One thing for certain, 900hrs is generally now a target threshold rather than a maximum - even on longhaul with most operators - thus expect to be away from home anything from 8 to 14 nights a month.....