For Shade, it takes around 2-4 hours. Because of the sketchiness of my manga (and general laziness), I tend to take a lot of shortcuts and don't really agonize over little details, since people won't look at them for long anyway. I only put in lots of detail for extremely important parts.
(For scenes with dialogue, barely any backgrounds. Backgrounds come when it's needed, like establishing the scene.)
For The Little Story of Jean though... around 30 mins - 1 hr. It's like that other series I work on when I want to cool down.
(I literally draw it straight on with pencil, scan it, then digitally water colour. It's so easy that I sometimes want to cry from happiness.)