How to properly judge a diet?

What is the proper time period to use to evaluate a diet?

Obviously there are going to be a day-to-day variance in what type of calories you consume and how many. Some days will be great, some will be simply OK and some days will be misses. So forming judgments on a daily basis does not seem practical or realistic.

What is the appropriate time bucket to aggregate your diet trends?

Should your diet be judged by the week? By the month? Somewhere in between?

Having more data is always better than having less data, so that the deltas become statistically significant. How would others recommend looking at it?

Also, how can I see the inputs into my food journal at any sort of aggregate level?