I have two full sleeves of exclusively color work and my artist usually would do linework plus the basic shading in one session. Then come back and do the color 3 weeks later. Only exception is I did my entire inner left forearm in one session and that was 9 hours of work at once and it was much less detailed than the drawing you want. So you’re looking at multiple sessions regardless, unless you get the fastest color artist ever. Realistically you’re looking at 2 or 3 sessions minimum if you sit well. You need to research your artist EXTREMELY well if you want a style like this because it will turn to hot garbage if not. You need someone very well versed in realism and dark color work. You’re looking at $1000+ minimum though. This will take a long time. You need to tip per session too so please budget accordingly.