str="Free slot start: 13:30:00 End of Free slot: 15:00:00"
intPos = instr(str, ":")
dtm1 = cdate(mid(str,intPos+1, 9))
intPos = instr(intPos+9, str, ":")
dtm2 = cdate(mid(str,intPos+1))
Assumes you'll always have the hh:nn:ss format with 8 characters. Could make it more robust by looking for...