Converting a custom date format (string) to a datetime

Question

I have a large set (100+ million) of observations with the date represented as a custom string format. We did not generate the date strings, I just need to convert the date

Answer 1

That DateTime string is valid for DateTime.Parse() (or .TryParse())

As for a truly custom string that .Parse() can't handle, you are probably correct, you'd need to pull your string apart and reassemble it in a useful manner.