BitTrex time format and time zone

Which time format/time zone is used by the BitTrex API?

I don't find an answer in the documentation https://bittrex.com/home/api

Example data: "Created" in https://bittrex.com/api/v1.1/public/getmarkets

For other crypto markets, I can use code like this:

let isoDateFormater = ISO8601DateFormatter()
var created: Date?
if let isoTimeString = row["Created"] as? String {
    created = isoDateFormater.date(from: isoTimeString)
}

Which doesn't work for BitTrex:

isoTimeString is set correctly, created stays nil since the format is not ISO.

While I could easily guess a working date formatter, I'd also have to guess the time zone. Is there a definitive documentation which time zone is used in BitTrex' API?

I have no need for swift code in the answer, a description is sufficient.

Edit I also asked BitTrex support but they appear to be overwhelmed by new customers as all exchanges.