English Translation
If you come back by five, you may go.
Very misleading translation - there’s nothing about “by” five here, it says clearly “at” five. A better translation would be “You can/may go, if you come back at five”.
To say “if you come back by five”, you can use “αν γυρίσεις ως τις πέντε” or “αν γυρίσεις μέχρι τις πέντε”.