Just wondering why?

Why do time of day helpers allow for more than 2 digits to be entered for hour and minutes?

You mean like this?

action: timer.start
data:
  duration:
    seconds: 75
target:
  entity_id: timer.foo

Or do you mean datetime? Can you show an example?

maybe someone wants 100 minutes, or 100 seconds

That is invalid. Seconds can not be greater than 59. Likewise for minutes.

And that is the reason.

At least in the context of setting a duration like @busman was doing in his example, seconds: 75 is not invalid... the action works.

Ah ok. There's definitely a limit somewhere. I remember the pushback when it was introduced, but not what for. Perhaps for: in state triggers?

Oh, why doesn't the UI element limit to two places? Good question -- the javascript probably should, although that still doesn't prevent from entering an invalid two digits.

If I enter something invalid I get this:

You see that, right?

Correct same error.

I think it should not be limited, if someone wants to enter 10 minutes in seconds, they should be able to, there should not be any limit on the number of digits for any unit of time.

That ship sailed years ago.

Perhaps for a timer or stopwatch application but the helper I am referring to is for the time of day. i.e. 2:45 PM. Besides that if you enter more than 2 characters or a invalid time it errors.

Reminds me of an old joke.

Patient walks into a doctor's office: "Doc, every time I kick a rock, my foot hurts".
Doctor: "Then stop doing that"

Ha! fat fingers I guess.