Can I say "until" instead of "by?"

Native speaker’s answer
Rebecca
No, "until" functions a little differently than "by!" "By" means no later than a certain time. Whereas "until" indicates the point of time something ends. Here, it could work! But the context would change a little. Saying "by Friday" indicates the deadline, "until Friday" would mean that the action of writing cards would end on Friday. Ex: I'll be in the area until Friday. => The person will no longer be in the area after Friday. Ex: I was at the party until five in the afternoon. => The person left the party at five. Ex: A: When did you get to the party? B: I got to the party by five in the afternoon. => The person arrived no later than five