Answer:
What does everyone know how to open but not how to close?
A precious stone, as clear as diamond. Seek it out while the sun's near the horizon. Though you can walk on water with its power, try to keep it, and it'll vanish in an hour.
At first, I am nothing. Add something to negate. Add again to oppose. Add again to find the time to draw. Add once more to find nobody at all.
Being able to interpret the letters on this screen proves that you have this quality.
Feed me and I live, give me drink and I die.
Those with eyes bigger than their stomach will definitely leave the restaurant with one of them. It is named after a house pet as well.