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 the first space after the second character after intPos the first time, if you need to. Probably don't.
Obviously dimension your variables and all that.
