When you train the chest you're automatically going to recruit muscles from the shoulders. So if you were to add another day of shoulder training, you're essentially going to be asking the shoulders to do more than they're capable of. You might get away with it for a week or two, but after that you'd notice that three shoulder days a week isn't the best bet.
Your best bet would be to rethink how you're training the shoulders. Can you write out your training split? Specifically, your shoulder routine. Also, if you would, post your training goals. I wanna see why you're stacking shoulders with legs. I can't imagine not doing legs by themselves.
I think a good way to train the shoulders is to mix it up. On any given shoulder day I might be doing reps from all the way down to 4, all the way up to 10-12, depending on the exercise. To me, good shoulders mean strong shoulders, but also, defined shoulders. But we can talk more about the actual training once you list your regimen.