I’m glad you got it working. Dropbox with HTTPS will work, you need to make sure that the link you use is to the raw file (instructions here). To test it, if you paste the link to your text file in your browser, you should see the contents of the text file, not the Dropbox download page.
The “updated at” label is built in to Dashing. Since you’ll probably want to change the language of that text on all of your widgets, I recommend following this advice and adding that little chunk of code to application.coffee.
Please post back and let me know how it goes.