Well, generally this question is impossible to answer as you haven’t given me enough information regarding what you want, where you want it, how big you need it to be, how detailed you want it to be and whether you want lining on it’s own, shading and lining or full colour!
Usually, it takes me around 3 – 4 hours to draw up a very detailed, large piece with intricate designs and shading added to colour (This is the largest end of the spectrum though) However, I often ask my clients to come and have a consultation with me first, so I know what they’re looking for and they can bring me any visual references. once I have done that, I will book them in around a week or so later and in the mean-time, if they wish to have a look at what I’ve done for them, I give them a window of two days once I’ve had a consultation with them.
If, for any reason, I have been unable to complete any drawings / sketches / designs for a client within that time, I will ALWAYS call them to let them know and re-book their appointment with them, but this rarely happens as I keep on top of my drawing / artwork and appointments in general.
I think you should go and speak to a reputable tattoo artist, who specialises in the field of artwork you’re looking to get and then ask him / her how much time he / she will need to properly draw it up. You don’t want to rush him / her, but at the same time, a decent and well prepared tattoo artist will have it ready for you well before your appointment. Please do not forget that most tattoo artist (Especially those of us who specialise in custom work) draw for around 70 – 85% of our free time, so therefore, we know our stuff (^_^)
Best of luck xxx