Are we talking about a shot of espresso or a mega large latte, etc... etc...?
Is the grinder ready to go with pre-ground coffee or do they grind on demand? Is the hopper empty and they need to add a new bag? Etc... etc... etc... ad nauseum!
You may as well have asked how long should one wait for a takeaway meal to be ready to go.
In any event... it could take less than a minute or more than four or five... it just depends on so many factors.