Thanks for your UK image. Sounds like you had to do some considerable gardening to get it!
While we would prefer the time part of the filename to be the mid-time of the exposure this is not essential and we’re happy with start, middle or end. Ideally the caption on the figure should state which one is used, particularly where the total exposure time is long. The time part is actually optional so 2014q2_20141230_ndj.jpg and 2014q2_20141230_1452_ndj.jpg are both valid. I use the time to distinguish between multiple images taken on the same day, or even sometimes multiple ways of processing the same image.
All the pages of the comet archive are automatically generated by scripts which depend on the correct filename structure. At present we are receiving 30-40 images of 2014 Q2 each day. This will no doubt increase so it does help us greatly if the filename conforms to these rules.