How to code a dynamic timer to expire 4 days after email sent

Hi,

I have been discussing with Sendtric about using their dynamic countdown timer. I want it to expire 4 days after the email is sent. I have been advised to use this
< img src="[http://gen.sendtric.com/countdown/ak2e8dpa4u?to=~today.date_and_time~+345600" style=“display: block;” / >
but it isn’t working. Any ideas?

Thanks