At this time of year the sun is up for 11 hours per day. If you ride all the daylight hours on Saturday and Sunday then that totals 22 hours (plus whatever you do on Friday).
Thus is you are going for 27 hours riding time and planning on taking stops during the day then you need to think about lights and how long they will last.
Another consequence of longer nights than days is that you might spend a lot of time in your tent.
Also, if you are planning on riding at night, try to plan your start time and riding so that you will not be pushing / carrying down Black Sail or Scarth Gap at night. They are tricky descents in full daylight.
Round the western side of the route there are not that many cafes / pubs so try to plan ahead for where you will get food / drinks / rests.