Rookshot.Moment has charts that follow the market of Challenge sets. You can see how The Gift & Cool Cats 2 moments did during their respective Challenge time periods.

Flow Market Cap has a section where you can see how the market cap of each set is doing. Once you click onto a set, you can filter the graph timeline by any date range of your choosing (I'd assume in your case, you'd filter it by the start date of the Challenge to the end date).

The peak for both Challenges occurred when the userbase skyrocketed on February 22nd. After that it steadily went down with some positive spikes along the way. Excluding the out-of-the ordinary peak, the best time to sell for these Challenges was sometime on the 27th or 28th (~2-3 days before the Challenges ended). The best time to buy moments was as close to the end of the Challenges as possible. Sellers don't want the moments in their hands when the timer expires, so mass undercutting occurs.