ForceLang, 155 bytes

    def s set
    s d datetime
    s z string.char 8
    s i 1
    label 0
    s z z+z
    if z.len=16
    goto 1
    goto 0
    label 1
    io.write z
    io.write d.toTimeString
    d.wait 9
    goto 1

 `datetime.toTimeString` is backed in the reference implementation by Java's `DateFormat.getTimeInstance()`, which is locale-dependent, so you can set your default system locale to one that uses 24-hour time.