I'm writing a novel and am looking for good software to make a timeline. The problem is that I don't know the scale of my story yet, so I'd like to be able to put in arbitrary time units. For example, rather than saying that something happens from 4/1/2012 to 4/3/2012, I'd like to say that the event happens from time unit 17-18 and then another event from 16-22, or something similar. I really don't want to have to use actual real dates. I found the timeline gadgt on Google Docs, but it doesn't have that feature. I really am looking for something that I can use online, ideally.

Thanks!