In Bergen last summer, my DW wanted us to go to one last attraction, the Funicular. I thought we would be cutting it close, but could not say not to her. Luckily, the Hop on Hop off bus came almost immediately, after we left there.
We got back on board maybe 15 minutes or so before the all aboard time. I commented to her that we cut it close. Her answer was that there were a lot of passengers in the boarding line behind us. I am assuming that they will not raise the gangplank while people are still in line, so that is my contribution to this thread.