ISO 8601 UTC timestamp with milliseconds in Objective-C.

gistfile1.m

NSDateFormatter *dateFormatter = [NSDateFormatter new];
dateFormatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
dateFormatter.dateFormat = @"YYYY-MM-DD'T'HH:mm:ss.SSS'Z'";
dateFormatter.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];