Countdowns and Clocks

Go to https://www.timeanddate.com/clocks/freecountdown.html and https://www.timeanddate.com/clocks/free.html

Configure your countdown or clock.

Be Sure to select 'Secure web page...'

Copy the resultant HTML

<iframe src="https://free.timeanddate.com/countdown/i5whsm8a/n179/cf12/cm0/cu4/ct0/cs0/ca0/cr0/ss0/cac000/cpc000/pcfff/tcfff/fs100/szw320/szh135/tatTime%20left%20to%20the%20New%20Year/tac000/tptTime%20since%20New%20Year%20started%20in/tpc000/mat%20/mac000/mpc000/iso2018-01-01T00:00:00" allowTransparency="true" frameborder="0" width="278" height="69"></iframe>

Use the embed edit function, select "Code" and insert the text you copied. 

Alternatively you can insert just the URL, such as:

https://free.timeanddate.com/countdown/i5whsm8a/n179/cf12/cm0/cu4/ct0/cs0/ca0/cr0/ss0/cac000/cpc000/pcfff/tcfff/fs100/szw320/szh135/tatTime%20left%20to%20the%20New%20Year/tac000/tptTime%20since%20New%20Year%20started%20in/tpc000/mat%20/mac000/mpc000/iso2018-01-01T00:00:00  

You can drag the result into the header if you wish.

You can insert it into the custom footer also. Example: https://sites.google.com/view/testbybob/

Another Method

From https://countingdownto.com/ See video here

Another one. From https://logwork.com/countdown-timer