How can I draw outlined fonts

There isn't anything built-in, but there are a few options...

• Just have a normal font, and render it a few pixels top left, top right, bottom left, bottom right in the background colour. Maybe a bit slower but it's simple, and it's what I've done on some other clocks (I forget which one now)
  
• Have two fonts, one big, one small - and then render the big one in the background colour, one character at a time and centered
  
• Store the font as an image with the background in. Since you're only doing numbers that's not going to be such a big deal. You can even store the 10 number image as 'frames' in one image rather than needing 10 separate images. I realised this wasn't documented yet, so added it in https://github.com/espruino/EspruinoDocs/commit/92b3957918b70182447f23536b6826fc6261e59b