Just a note that you can group your nn:nn:nn at make length match for it. as I did below.
Code:
alias retest1 {
  var %s = beginning text 00:0:00 middle text 00:00:00 end text
  if ($regex(re1,%s,/(?:((\d\d?)((?1)|\:|\s|){3})|([a-z].*?)(?=\s0|$))/gi)) {
    echo -a (Before): $regml(re1,1)
    echo -a (Match1): $regml(re1,2) 
    echo -a (Middle): $regml(re1,5) 
    echo -a (Match2): $regml(re1,6) 
    echo -a (Ending): $regml(re1,9)
  }
  else { echo -a No Match }
}

/(?:((\d\d?)((?1)|\:|\s|){3})|([a-z].*?)(?=\s0|$))/gi