that would be the most user friendly way. And probably the way the Mods would like it done.
IF you are VERY computer savy you could try to just find where the date is in the code in your signature and change it to your new date. That said THIS IS NOT RECCOMMENDED as if the script is changed incorrectly it can throw the WHOLE SITE off, that is why they have the page that creates the script for you.
So I would just recreate it and replace the current script in your signature with the new script created.
Found the thread with how to get the timer code (in case you needed a reminder, I know I did) it is HERE