Traditionally cooks chanted shlokas and verses from our scriptures while making Naivedya. Generally, one should have a bath before cooking for the Lord. Everytime / anytime during the cooking process, hands must be washed if comes in contact with the mouth. In other words, one should consciously not put their hands/fingers to their mouth. Another important point is that the food should NOT be tasted at any stage until offered as Naivedya.
The timings are approximate and have been given as guidelines only