If someone does not believe the world was created in 6 days, or thinks that the animals, or certain ones ate meat, is that no doubting what God can do? God, the creator of all things, can do anything, he is not limited to what we can imagine.
Second, we have to understand that the bodies that Adam/Eve, and the animals had back then were FAR superior to our bodies. The plants back then which they would of eaten (as is recorded, God gave them fruit to eat) would of had many more nutrients etc. in it that would of sustained life much more beyond what plants can do now. Look at how long they lived back then, they died of accidents or old age. AFTER the flood the whole earth changed and the atmosphere did to, making the earth a much harsher environment to live in.
So, keep in mind and make sure you are not doubting what God can do. If God wanted us to think it was more then a day maybe he would of used a different term?