It doesn't accept "Until morning"?
Ignoring the fact that Tot morgen is a standard greeting for a second: morgen means tomorrow, in de morgen, 's ochtends or 's morgens means in the morning. Tomorrow morning is morgenochtend.
It should accept "Until tomorrow", and also "Til (or till) tomorrow", which might actually be the commonest way we say this in England.
These days I think it would be more common to say "See you tomorrow". To say "Until tomorrow" when saying goodbye to someone sounds a bit old fashioned to me.