Console.WriteLine(TimeSpan.Parse("23:00:00").TotalHours);
Console.WriteLine(TimeSpan.Parse("24:00:00").TotalHours);

НС>Console.WriteLine(TimeSpan.Parse("23:00:00").TotalHours);
НС>Console.WriteLine(TimeSpan.Parse("24:00:00").TotalHours);
НС>

if (inv)
{
    if (raw.FullHMSMatch(TimeSpanFormat.PositiveInvariantFormatLiterals))
    {
        positive = true;
        match = TryTimeToTicks(positive, zero, raw._numbers0, raw._numbers1, raw._numbers2, zero, out ticks); // Вот это сопоставление не проходит, так как _numbers0 >= 24
        overflow = overflow || !match;
    }

    if (!match && raw.FullDHMMatch(TimeSpanFormat.PositiveInvariantFormatLiterals))
    {
        positive = true;
        match = TryTimeToTicks(positive, raw._numbers0, raw._numbers1, raw._numbers2, zero, zero, out ticks); // Поэтому идём сюда. В этом формате те же разделители и то же количество элементов, отличие только в их числовом значении
        overflow = overflow || !match;
    }

    ...

}

private static bool TryTimeToTicks(bool positive, TimeSpanToken days, TimeSpanToken hours, TimeSpanToken minutes, TimeSpanToken seconds, TimeSpanToken fraction, out long result)
{
    if (days._num > MaxDays ||
        hours._num > MaxHours ||
        minutes._num > MaxMinutes ||
        seconds._num > MaxSeconds ||
        !fraction.NormalizeAndValidateFraction())
    {
        result = 0;
        return false;
    }

...

    return true;
}

[ws][-]{ d | [d.]hh:mm[:ss[.ff]] }[ws]

If the s argument is not a day value only, it must include an hours and a minutes component; other components are optional.
If they are present, the values of each time component must fall within a specified range.

For example, the value of hh, the hours component, must be between 0 and 23.
Because of this, passing "23:00:00" to the Parse method returns a time interval of 23 hours.

On the other hand, passing "24:00:00" returns a time interval of 24 days.
Because "24" is outside the range of the hours component, it is interpreted as the days component.