It's implied they generate gravity on the ships by burning the engines* and the engines seem to burn all the time, so you can assume for half of every trip they are accelerating towards destination and the other half they are decelerating again.

Orbital mechanics seems to only apply when convenient, e.g. an orbital mirror around a moon is damaged and "falls" straight down. I don't think that is accurate, even assuming the loss of atation-keeping thrust.

* Not real gravity, but you can't tell the difference between gravity and acceleration. And they also account for high-G manoveurs being difficult/deadly for humans.