懂英语的人注意了

作为介词时可以解释为"up to "作为连词时可以解释为"up to time when"

until - up to the time that; to the point or extend that; before ( a time or event); (often preceded by up)in or throughout the period before
You can't go home until you've finished cleaning up.
It wasn't until last year did they see each other again.
He hadn't heard from her until a week ago.

up to (a time) that
before (a time or event)
in or throughout the period before
earlier than; before

till~~~
up to~~

up to some time

till;to the time