"A couple weeks from now" will be too late. Here's what I mean:

Committing to one day a week to phone bank or knock on doors for our candidates will help our candidates win on Election Day. 

If those dates don't work, let us know what dates work for you. We're phone banking Monday through Thursday, and walking door-to-door every Saturday.

Now is the time. We need your help now, or else we will miss our chance.

Best,
Jonathan