Germans have a hard time with by
and until
-> Use by
for actions that will be or must be performed at some moment before a time.
-> Use until
for actions that continue and stop at a time.
Examples:
- I work until 17:00. (working happens continuously)
- I will leave by 17:00. (leaving happens once)
- Give me the report by 17:00. (giving the report happens once)