It's actually simpler than you're probably thinking.
To remove it completely, go to your User CP and edit your profile. You'll see "Your Signature" next to a box of text. Just erase the stuff in the box of text that you don't want to have in your signature line.
If you want a new countdown clock, I THINK that you need to erase the old one and get a new one, which you can do here:
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