used Mug of Fulfillment which is supposed to double food and drink duration. used 10 hour food and drink. Duration not doubled from 10 hours.
There are no 10 hour duration food or drinks. The mug doesn't increase your food/drink duration because you're already at the maximum increase before using it.
so the 10 hours you see on food and drink is already showing that because you used the Mug, whatever food you ate has a shorter duration normally without any boosts
You used a 5 hour food and drink, which tends to be the max duration available and it was boosted to 10 hours due to the mug.
(FWIW, the confusion is probably because you can get to 100% duration increase without the mug if you take all the relevant AA for food/drink durations. So they probably did see 10 hours before clicking the mug. That's why I said it the way I did above; though it is certainly possible they did not.)
Just as a suggestion, perhaps consider changing the text of the items that boost food/drink duration to say "up to a maximum of 10 hours".
I don't believe 10 hours is a hard maximum duration; It's just that the longest base duration food/drink available is 5 hours, as far as I am aware.
Funny how that works. My answer was based on testing it on 2 characters. One clicked the mug, then opened broker and looked at lvl 125 food, the highest I saw was 10 hours so bought that and ate, no more increases of course. Another character first opened broker, bought the same food (which showed 6 hours + with whatever AA's she has on), then clicked the mug and that same food showed then a 10 hour duration, ate it, no more increase of course. I find it really interesting, and great to know we can reach max without mug
