How much difference does a week make? September/October

I think, especially with erratic climate, that time of year can vary greatly. But to be honest, for urban areas, as long as you are able to walk around comfortably, not excessive rain, then things will be great. Crowds? Yeah, I think they will diminish slightly, but all of those destinations see constant crowds. Of course, any trends are out the window with covid, crowds in peak times seem to be low, but then, when restrictions drop, crowds come out of the woodwork. I do not worry too much about it, crowds in September seem manageable, October more so, so just jump in and do it.

A week will not make that much difference. Slightly shorter days -- that is about it. Weather a bit more variable as Fall approaches. Could be warmer or colder. If delaying a month, then the difference would be greater. Not much change in crowds.

The weather is generally good on Central Europe in either period. A few more universities will have begun their term in the later dates and that might help a little with the crowds.

@Paul and @Frank
Thank you! A good "I do not worry too much about it" is good to hear sometimes!

@James E. Good point about universities!

@joe32F

You have kept your local secret, so how much different is the weather on Oct 5 and Sept 29 where you live?

You can probably expect the same sort of variability at your proposed destination(s)

((wide eyed)) You mean, Europe is just another land mass on this same ol' rock? Haha, well, what can I say? It is easy to think of Europe as a different universe to the point of defying common sense, I suppose!

That said, I live in PA now. (Lived in Florida and South Carolina growing up.) Here in PA, the weather changes precipitously and without warning. Last April, it was both 21F and 81F-- in the same week. Literally. While we had the occasional hurricane down South, the weather changed more slowly and within a smaller range.

There are lots of factors. Distance from the equator, elevation, bodies of water, city/country, shade cover, etc... and still, sometimes the weather in certain places defies logic. It rained nearly every day in Florida and we held at a steady 90 for weeks. It rains one afternoon in PA and the temp can drop 20 degrees.

Seems the easiest way to figure it out is to ask someone who's been there in various seasons. So, I know everyone is dyyying to know how the weather is in Amish country or Steeler country and I am happy to return the favor with a detailed analysis. (You wouldn't believe the crowds we get in the summer. At least 9 or 10 other cars on my block for local restaurants.)

Insider tip in case you don't watch CNN: Our bridges aren't so hot, but good luck getting anywhere without going over one (or 5).

The month of September is rather nice the places you plan to visit. Crowds should be less than in the high Summer season.

I doubt if one week will make much of a difference.

That period does include the Octoberfest in Munich, but you didn't list it to visit.

We have done two transatlantic cruises from Europe to the USA, that departed from England and Denmark in late October. Both of those trips we did a pre-cruise self tour and found it a bit chilly, but not so bad for the weather. Also, crowds were less.

Sleight, I'm very weather-focused. I really like the timeanddate.com website. It has actual, day-by-day, historical weather data for most cities of even moderate size, The information usually goes back about ten years. I generally check the most recent five years, focusing on the question: How cold can it get during the hours of the day I might actually be outdoors?

For precipitation, I take a shortcut and go to a city's Wikipedia entry and look for the colorful climate chart showiong monthly averages. The available data varies, but usually you'll find the number of days each month with precipitation and the total amount of precipitation for the month. Monthly averages aren't great, but I really don't know how to evaluate day-by-day rain data. If you see very similar precipitation figures for September and October, you can figure ignore rain in your timing calculations. I would caution you that those Wikipedia charts seem to cover a time period that cuts off in either 2000 or 2010, which I think isn't great, given that weather seems to be getting wackier.

Do you think shifting from Sept 7-29 to Sept 13- Oct 5 will have a noticeable effect on the crowds (and weather?)-

Nope.