At the end of a work day, someone might say, "That's it for another day." It simply means, "another day of work is finished." It is usually used in the case of a repetitious job; a job where any given day is much the same as any other.

Often times you will hear "that's for another day" which means we will do that some other day, or "that's it for today", which means you're done for the day. I have never heard "that's it for another day", but that doesn't necessarily mean it isn't common somewhere else.