“改日”的意思是换一个别的日子，不是现在，也不是今天。

The meaning of "改日" is to change to another day, not now, and not today.

今天没时间的时候，我们常说“改日再说”或者“改日再见”。

When we don't have time today, we often say "改日再说" or "改日再见".