i know it's possible and I have done it myself before but there are many factors that contribute to the results. moon, street/building lighting (basically light pollution), and clouds that reflect lights from (light) polluted areas.
According to Snoweagle, he did it in a pitch dark environment. further more I believe he shoots film. at 5 mins I believe reciprocity failure would have kicked in as mentioned by Isisaxon. But it's good to know that 5minutes would produce such results. It's good experience sharing.
So back to the question, how to know the exposure time in bulb? I use digital, so I can afford to test. I do a 2 minute test with f/8 at ISO400 and work from there. Since my cam can only open for 30mins, I will just aim for a 30min exposure.. anything under or slightly over can be corrected with post processing later.
If you look at singastro, there are some pictures that have showed night scenes turning into more like pre-dawn instead of 'day' pictures.