As far as a time line goes, I sent out my submission on 12/10, received an acceptance on 1/09 and it is going to be published 2/28. So a little less than 2 months from submit to publish on that one. Obviously one example does not show a trend, but I thought it would give some insight (plus its my first puzzle, so I don't have anymore data).
If a puzzle is good, a publisher will take it, but if he takes 8 in one week, maybe he only takes 6 the next since the puzzles aren't as good of quality. Also, if a publisher gets lots and lots of puzzles that they would normally accept, they may up the standards for acceptance. Using the rule of thumb that they take 7 a week is an easy way to make some statistics.