10:50AM

First Measurement 

The first measurement I took was at 10:50am. I started all three of the flowers with 200ml of water. After about an hour, the room temperature flower was at 195ml of water, the cold temperature flower was still at 200ml of water, and the hot temperature flower was at 180ml of water. 

So by the first measurement, my prediction was incorrect. Instead of the cold temperature flower drinking the most water, the hot temperature water had drunk the most.