It varies from company to company. On my Gameinformer, I had 2 weeks from concept to line arts to final colors. With this piece, they gave me plenty of time but there was a lot of back and forth to make sure each character "felt" right and there was enough space and balance between the characters and the background. It was very challenging and if I hadn't already spent the last 10yrs drawing and coloring multi-character pieces I don't think I would have had the creative stamina to see this one thru.
The studio was totally supportive but I'm rather hard on myself. I put all other projects aside for an entire month to get this done. I can't tell you how long it ultimately took hours wise, because to count them would just add more pressure to myself mentally. I just tried to focus on each character as they came up, adjusted for revisions and moved on to the next thing. Then there was the coloring setup, then the colors... THEN I had to digipaint the bg.
It's a lot of effort, so if you feel like it's hard, it is. Don't expect to be done in under two weeks unless yur a creative genius. I'm most certainly not lol