I do a slice of life comic where each page is an independent story. And all of my first comic pages took a really long time - like ridiculously long - all of them 20 hours or more, even if they were really simple, because I was experimenting with style and colours and brushes, looking for the right font, testing different formats, etc. And after I had made a decision, I could go back months later and make changes (I have a pretty large buffer, not even half of my oldest stuff is posted yet). I still see things now that I'll probably change before I publish.
With the newer stuff I'm making now, the comics that I think are among my simplest, I would say I spend about 2-5 hours. Colouring always takes way more time than I expect it too. With the comics that are neither my simplest, nor my most complex, I would say 8-10 hours. When I do stuff that requires a lot of colouring and details, it can take up to 20 hours or more
All time estimates here include sketching, inking, colouring, deciding exactly what to write and figuring out the text layout. And the text bit is also one of those things that always takes much longer than I expect it to...
I've already improved my efficiency quite a bit, so hopefully I'll be able to be even more efficient if I keep creating on a regular basis
Having a plan and a proper sketch to start out with helps the rest of the drawing process immensely!