Difficult to say without seeing some sort of draft idea, because designers, like most professionals, charge by the hour, and the time could vary according to complexity, and/or number of versions required for use in different circumstances, like print, online/web, colour, mono, use on transport, etc.
It’s not a one-size fits all situation, or shouldn’t be, if the design is to function properly.
It’s something I’ve done in the distant past, but I was never that creative, just good at finished artwork, and I’ve neither the time, nor inclination, to get involved again.