1	String passed in does represent some amount of time.
0	String passed on does not represent a time.

To be more exact, not only does the string have to have the form hh:mm:ss --
1. Each of the mm, and ss consists of two decimal digits.
2. The number of minutes must be below 60.
3. The number of seconds must be below 60.
4. The hours part must have at least two digits and may have more than two.
The string can optionally begin with a minus sign to indicate a negative amount of time.
In a future release we may allow for more flexibility. For the current release, we are keeping it simple and straightforward.