"john씨는 7시마감이세요" => John 씨는 7시(에) 마감이세요.
As Matty explained, it means:
1. John, your deadline is at 7 o'clock. (if speaking to John)
2. John's deadline is at 7 o'clock. (if speaking to someone other than John)
January 8, 2016
Hi Brianlee, I'm not a native speaker, But i think the sentence means:
john씨는 7시마감이세요 = John, the deadline is at 7 o'clock.
John 씨 = John (as the subject)
7 시 = 7 am/pm
마감 = A deadline, an expiration
이세요 = 이다 (+ Honorifics).
Hope this helps!