We bought an Eurail Twin flex pass for 5 days for our trip to Germany. We shall arrive in Frankfurt, go by train to Bacharach, and then, after two days, by train to Berlin.
I want to start using the pass when we travel from Bacharach to Berlin (so, for traveling from Frankfurt to Bacharach I'll buy normal tickets). The pass should be validated before first trip.
My question is: can be the pass validated two days before first trip, or this must be done in the day of first trip?

I ask this, because in any case in Frankfurt we go to tickets office to buy our ticket to Bacharach, and I want, in the same time to validate my pass, even it will be used for the first time two days later

A travel agent can validate a Eurail pass prior to travel, so I imagine this could be done at the train station as well.

In the past, I've found that the validation at train stations is not at the same window as where you buy tickets (just fyi).

If you don't validate the pass in Frankfurt, it shouldn't take very long to do it in Bachrach (generally there isn't a line, you just go get it stamped and hop on your train).

Please, correct me if I'm wrong fellow Fodorites.

You can indeed validate the pass several days before you use it. You must be accurate in writing in the first date of use however, which does not need to match the validation date.

Here is something to look out for -- probably not a problem but it did happen to us. A conductor on one train stamped our pass one morning. That afternoon when we boarded another train the conductor started to stamp another spot and I said no it had already been stamped that day. That's when we realized that the morning conductor had his stamper set to the wrong date, several days before. So the afternoon conductor was stamping another day. We took the passes to the Berlin Euraid office and got them to issue new ones. We had our plane tickets and our stamped passports to prove we hadn't even been in Germany on the date that was stamped in our passes.

So be sure to look at the stamp each conductor does to make sure it is right. On some trains, I suspect they may not stamp that many passes?

Thank to both of you. Now it is clear to me.
I made the seat reservation for some trains - all long trips when we are with the luggages - but I do not know why I can not do this for the trip from Berlin to Cologne. Is written something in red, in German, I did not understand what and had not time yet to translate (with Babelfish).
I hope to be able do make this last reservation tomorrow, it is the last thing to be done before our trip, that will start on Friday.

Each time I had a rail pass I simply filled in the date with a pen.
There is a special space on the pass where you have to put in the first date of travel. You can write this whenever you want, but in any case before you board the train.
That's validation of the pass.

The rail pass will be usable for some time period (2 months?) after it is validated. So, as long as you are not going to be in Germany using the pass for 2 months, it can be validated at the Regional Bahnhof at at the Frankfurt airport when you get there.

It is very important that you do it there. The last time I was in Bacharach, the station was "un-manned", i.e., there was a ticket machine, but no counter where a person could validate your pass.

I didn't have that exact kind of rail pass, but for the one I had, writing in the first date of travel was not the same as validating it. YOu had to validate it as a separate step at a window in the train station.

Yes Christina, I think that GabrielTraian is wrong. It is a special place on the ticket for validation.This is why I asked if I can validate it two days before my first trip. My pass can be used for any 5 days from 30 days, and it can be used 6 month from the date when I bought it.

Thank you Larry for advise, I also was afraid that Bacharach can have a small station without an office. I'll maake sure that I'll validate the ticket in Frankfurt.