A breakdown of à demain
If I have this correct à mean on, in or at.
Demain means tomorrow.
When put together and directly translated into English it is 'on tomorrow'. This reminds me of that old English saying 'on the morrow'; which means 'see you tomorrow'.
Is this right?
Oh okay. I made my assumptions from the mouse-over hint-box when I was asked the question. Duolingo gave on, in and at for 'à'. If until is part of the translation of 'à'; then that makes more sense.
Here, 'à' cannot mean 'on', nor 'at'. It means 'to'.
The archaic spelling of 'tomorrow' is 'to-morrow', which meant: 'to (the) morning'.
'Demain' comes from the Latin 'de mane', which means 'at/in the morning'. So 'à demain' means 'to the morning'.