how to turn seconds into h:m:s？？？

in what? what language?

verilog.......

In vhdl, you can run multiple counters on the 1 sec clock edge:

if(Seconds /= 59) then
        Seconds <= Seconds + 1;
else
        Seconds <= (others => '0');
        if(Minutes /= 59) then
              Minutes <= Minutes + 1;
        else
              Minutes <= (others => '0');
             if(Hours /=23) then
                   Hours <= Hours + 1;
             else
                   Hours <= (others => '0');
             end if;
        end if;
end if;

We don't expect to use the "/=" ,it causes delay.

It is a comparator either way (= checks all bits, /= checks all bits). Any difference in implementation or length of paths is target/tool dependant

ok