“Nineteen past eight” seems like a very strange way to tell the time to me, it’d have to be specified as “Nineteen minutes past eight” (there are exceptions like “five past”, “ten past” and “twenty past”, but “nineteen past” sounds weird), but maybe that’s a dialect thing (my dialect is mostly some form of British).
Not very regional. I've live in CA, CO, and MO. Both "nineteen past eight," and "nineteen after eight," are fully interchangeable. I've never met or talked with someone who had a strong preference (would considered one of the two wrong) for either one.
It's just another case of the Duolingo people not being fluent educated speakers of English.
It's a great language learning program, I paid for a year, I recommend it every chance it get, but it could still use some improvement. They need language editors who are fluent and well educated.