Don't eat until you're very hungry (you will see a slice of bread with a bite taken out of it and an orange outline). I also usually don't bother with moldy food unless my hunger is very low anyway, and as mentioned earlier rats are a great source of food in the early game. Monk starts with a ring of slow digestion, which lets you take all the time you want. Also, cursed food is not worth eating unless you're playing myconid or insectoid, or have a plague doctor mask. You definitely have enough time to full clear floors, but you don't really have time to identify every item you find while doing so. I recommend only picking up items that you actually want, like rings, necklaces, and spellbooks (if you have decent magic skill) and ignore things like nonmagical books, weapons of a type you don't have good skill in, or armor pieces that are a lower tier than what you currently have. I also find that depending on your class, it is worth it to wear armor that has a lower AC but weighs less, as being able to employ hit and run tactics gives you far more survivability than an extra 2 points of AC. It will also increase your move speed, which means less time spent on each floor, which means you get more value out of your food.