is it simply, get into the jhana, come out of the jhana, introduce the object of insight?
I generally used dry insight most of the time but if I enter jhana then the process is - Enter jhana and abide there before beginning insight practice, so you're staying in jhana and noting within it. Being in jhana suppresses the hindrances which takes away some of the usual distractions you might encounter.
are certain jhanas more helpful for certain insight stages?
I don't know, personally I look at the factors of each jhana and choose which one to begin from as each have their benefits. My favoured way to go about it is to enter 4th jhana and begin from there due to the equanimity, pleasure and mindfulness inherent here. This, in my experience, makes going through the dukkha ñanas much less unpleasant and reveals some subtle stuff which may not reveal itself at first through dry insight.
Try this link about the
factors of each jhana.how do typical sits go when employing jhanas to insight?
I like to think that using jhanas 'peels back' certain strata of mind and allows more detailed exploration. Here's some links to my own practice threads on here and KFD so see of there's anything of use to you there.
First practice thread.KFD practice thread.i read a post on kenneth folk's wiki regarding the parrallels between jhanas and nanas which provoked the question of whether or not 3rd jhana, for example, would not be a better place to hang out and launch an insight investigation from when one is at the equanimity level of nanas.
Once you're in equanimity you're in the 4th vipassana jhana anyway, don't worry about entering specific jhanas at specific times, remember the comment about jhana leading to insight. Enter jhana before beginning insight, or alternatively enter jhana if you're feeling a bit rough or tender during a sit 'cause there's no point in burning yourself out.
it could be though that that was referring to your point about a nice refuge from the sometimes difficult passages but that amounts to the same thing methinks..slowing down the progress. or?
If you spend all your time dwelling in jhana then progress will be slower, however it's worth knowing that progress is still possible. Don't let progress become a stress, there's no point in it as it will happen naturally if you practice well.