I just wait until my babes can feed themselves (7 1/2 months, 8 1/2 months for the youngest two), then offer pretty much whatever/whenever, with the exception of raw tomatoes, honey, nuts, or grains. I don't wait days between introducing new foods. There are tons of things I give him that have multiple ingredients anyway. It would be hard to figure out which ingredient in the stew/chowder/soup etc. caused a reaction. If my baby rejects a food, I take that as a sign that they aren't ready for it/might be allergic to it/don't like it. So I'll wait a few months and try that food again.
No one in my family has food allergies, and none of my kids have been allergic or intolerant to any foods they've eaten, so I feel comfortable scrapping the waiting between new foods.
Plus, I have a hard time remembering when I last showered. It'd be almost impossible for me to remember what food my kid had 4 days ago.