It is indeed time consuming if you're talking about doing deep stacks with more than a handful of shots, and yes, movement in the subject often spoils deep stacks. It is quite possible to stack a few shots handheld, so if you are doing that, you really only need as much time as it takes to fire off the shots. I have seen many people do this successfully, and this is probably the best place to start.
Personally, I prefer to do deep stacks (30-80 shots) taken from a tripod of a subject that is on a base that is either perfectly still already (e.g., a rock or tree trunk) or forced to be perfectly still by a clamp attached to a second tripod. If you are using really good stacking software (e.g., Zerene Stacker), the subject can move a little bit, and you can still make it work. However, most stacks of more than 15 shots will fail due to subject movement. It's just the name of the game. In terms of time, I have been known to spend 20-45 minutes with a single subject on some occasions, and almost never less than 10.
The key to keeping subjects still enough for stacking is to do your stacking right at sunrise or sunset. You can do stacking during the day as well, but you will have a much harder time finding a subject that will stay still long enough for a stack of more than a small number of shots. Sleeping insects are still insects.