My observations are that it's totally random. At first I thought it was measuring the time you spent reading the hub, but that didn't pan out as I read some without the bar filling and skipped over some where it did fill up.
Newbies can hop hubs. I hopped some my first day. I think it's just a matter of discovering the link in your account page. Most of the hubs I hop appear to be just published, but many are by established hubbers so I think your hubs just go there for the first day or two after you publish them.
Hopping is to help with quality control. Voting up and down helps the new hubs get a more accurate score than word count or some other computer generated score can do.