ISTSTIME(<C time string>)
 Evaluates whether a time string is valid in format and contents.
 Returns <expL> true if <time string> is valid, otherwise false.

 <time string> is in the format "HH:MM:SS", the same as returned
 by the TIME() function.

 Valid times are in the range "00:00:00" to "23:59:59",
 or 12:00:00 a.m. (midnight) to 11:59:59 p.m. (one second before midnight).

 * Validate user-entry time string
 m_timestr = "  :  :  "
 @...SAY "Enter time as time string:";
     GET m_timestr PICTURE "##:##:##";
     VALID ISTSTIME(m_timestr)


             Placed in the Public Domain by Tom Rettig Assoc.