The amount of xEgg in the Chicken Coop will not change. But the amount of Egg it represents will.
As fees are collected they are converted to $EGG and distributed proportionally across holders in the xEGG pool. So when you withdraw your xEGG back into $EGG it will be worth more $EGG than when you put in.
These rewards are slower to update (because they cost a lot of gas) and so you should expect them to update, on average, once per day.
Currently there is no way in the UI to see the level of rewards until you withdraw. The team is working to fix this.