Regular expression where part of string must be number between 0-100

Question

I need to validate serial numbers. For this we use regular expressions in C#, and a certain product, part of the serial number is the \"seconds since midnight\". There are

Answer 1

I don't believe this is possible in regular expressions since this isn't something that can be checked as part of a regular language. In other words, a finite state automata machine cannot recognize this string so a regular expression cannot either.

Edit: This can be recognized by a regex, but not in an elegant way. It would require a monster or chain (e.g.: 00000|00001|00002 or 0{1,5}|0{1,4}1|0{1,4}2). To me, having to enumerate such a large set of possibilities makes it clear that while it is technically possible, it is not feasible or manageable.