You didn't mention how much use the battery has had in that 11 months but rechargeable batteries will lose capacity over time. One minute difference could be caused by wind direction and speed; even less air density caused by warm weather will make the Mavic work harder to stay in the air.
The values are close enough that I wouldn't worry about it. It would be interesting to fly the same route 3 more times to see what average you get. Due to minor differences in each trip, the last trip may get better performance than the first.