This was a kind of random achievement to get. but i was online with a friend, and we just decided to try it. First time we did it we failed. We went to blackwater and waited until midnight, we then set a waypoint and then rode all the way down to the other location.
We got there at sun rise and realized that we did it in the night!
Anyway. in case you guys want this trophy, this is how we did it. First you need to get to Blackwater. If you use the transport fast track. Make sure you leave the town to the great plains and return, so that 'Blackwater' appears in the corner. Now you should wait until sunrise which is at 6.00am. Now set your waypoint (or not, depends on how well you know the entire map i guess...) And ride there. Make sure you get to point b before sunset, and you'll get it fine.
Just thought i'd clarify that because the description for this was a bit vague...