@QAQ
Hi there!
Don't worry about being lazy😊 If weekends aren't made to be lazy, what are they for?
Besides, you're talking to the laziest person alive 😜
For your question, i would say that the difference is a matter of time.
Let's say i'm phoning to a friend, and that we agree to meet later on: if we meet in a short period of time, we'll use "à tout à l'heure", but if we meet later (like, at evening), we'll use "à plus tard".