The most compact ISO-8601 format doesn’t use any separators within the date or time values, just to designate where the date field ends and where the time field

The most compact ISO-8601 format doesn’t use any separators within the date or time values, just to designate where the date field ends and where the time field begins, and that’s with an ASCII “T” character. So long as you know what the other fields are and what their sizes are, you don’t really need separators.