=MOD( FLOOR( NOW()*100000*FREQ; 1; ); 2 )
This formula checks if the time is even or odd. FREQ is the frequency of the clock in Hz. Update the clock by holding the button that is assigned to recalculate everything. (I think it is F9)
As an alternative, you can select an empty cell and hold Ctrl+R.
For convenience, you can assign the clock cell some name like "CLK".
You could also create a manual clock and a button to switch between the two.
All the other things...
...will probably be listed in this reply.