EDIT: As BanjoRebel pointed out apparently the trailer can spawn in different locations.
I will leave my map up for those who have it spawn in the center spot and want to try it in one shot, but each objective can be done on it's own as long as you complete the main objective.
The 3 bonus objectives in this challenge are:
1) Complete during the night (Finish before 6 AM, which is roughly 12 minutes I think.)
2) Reach all Watchpoints (2)
3) Find the fluorescent flowers
Here is a screenshot of where the flowers are:
And here is the path I took. There may be better ones but I finished with plenty of time to spare even after looking for the flowers. (Green was my starting and Blue after I got the flowers)
Generally you want to stay on the green and brown areas as you can easily get stuck in the water (especially when you have the trailer.) You can use the many trees to help speed you up or pull yourself out. Some of the smaller trees will break easily with the winch but still can pull you a few feet which can either free you or get you close enough to another larger tree.
Also, it is best to leave the trailer for last as it will slow you down a lot.