I have been told to pitch an Air conditioner level to a 1/4 bubble pitch to the outside. What exactly is a 1/4 bubble? I would think that depends on the length of the level used.

The length of the bubble no matter how long the level,1/4 of that bubble
A little off level so as rain and condensation water can run out,

I agree with wmproop. Quarter bubble is the same on a six inch level as a 4 foot level. Quarter bubble is just to let you know you have slope. However, a better procedure, if you are talking about a condensate drain line, would be to slope the pipe a 1/4" per foot.

Now that I reread your question, are you talking about a wall a/c unit. In this case, you just want to break the bubble so that you know you have slope towards the drain of the ac unit. Doesn't have to be much, it can even be level, but a little slope is preferable. Install instructions should give you clear installation instruction.