absolutely NOTHING wrong with doing them on a different day.
Think about it, you work chest which using the tricep also , so when you get to tricep, you can't work them as heavy since you have already hammered them with chest.
same thing with biceps, already hammered back which uses biceps.
I do this, 2 week rotation. first week chest & tri's together, back & bi's together.
next week, chest alone, back alone, off day, then arms together and that day on arms i train them heavy.