If you want to add Hrs into the mix you can use the following.
I built off of Mike's existing code, so as not to grab all the credit.
numbervar sec:={Sec value here};
numbervar nMins;
numbervar nSecs;
numbervar nHrs;
stringvar sMins;
stringvar sSecs;
stringvar sHrs;
nHrs:=truncate(sec/3600);
nMins:=truncate(sec/60) - nHrs * 60;
nSecs:=remainder(sec,60);
sHrs:=totext(nHrs,"00");
sMins:=totext(nMins,"00");
sSecs:=totext(nSecs,"00");
sHrs + ":" + sMins +":" + sSecs