I have been searching here and elsewhere to find an answer to this question and I can't seem to come up with anything more than a rabbit hole of complex mathematical equations. That or my searches are not leading me to the correct answers. I have only ever taken untracked short 10-15 second exposure subs with a wide angle lens and DSLR for Milky Way images. I have been looking at many different options and after a lot of research and deciding to stick with my own camera gear for a while I decided to get a Star Adventure 2i Pro with a ZWO 30mm Guide Scope and ZWO ASI 120mm-S guide camera. I already have a good tripod for bird photography that I use with a gimbal head and my 150-600mm lens. I had debated on whether to get an EQ6-R Pro and use my camera gear until a later time when I can add a scope, but I decided that the Star Adventurer is quite capable and will give me a lot to do while I learn. So that is where I am and where I am getting started on soon once everything arrives. So I have been watching lots of videos and reading lots of thread.
I have already purchased Charles Bracken's Deep Sky Imaging Primer and Allan Hall's Getting Started: Long Exposure Astrophotography books. I have not yet read them cover to cover, I am working on Allan Halls right now as it seems easier to digest and written in a manner well suited to a beginner.
With that in mind here is my question.
I understand this is always going to depend on what gear is being used and where in the world you are and what the light pollution is in that area. With that said is there any easy rule of thumb for how long the total exposure time should be for any given target?
I have seen examples tossed around various threads here with images of with a total time of 10 minutes, 30 minutes, 1 hour, 4 hours, and many more. Is there such a thing as too much time?
I am aware that the individual subs would be better if they were longer. So 10 x 1 minute subs are better than 40 x 15 second subs.