constant speed

after breaking it in, it´s OK to drive it at say 75MPH with cruise set, for an hour or maybe two, right? because everyone says don´t let it run at a same RPM for too long, just wondering.

some of this depends on what is "after breaking in"

at LEAST 20K and probably more like 30 to 40K before a complete run-in of the engine is accomplished.

setting the cruise for 75 is not harmful, just blip it up and down, say every few minutes or so to nearly 80 indicated and down to 70. the superslabs i drive on here in Texas have so much traffic that one cannot maintain any constant speed for more than 5 or 10 minutes at a time.
A trip from LA to Palm Springs or Las Vegas might be different.

You should be fine running on CC for hours at a time once you get past the first 1,000 miles or so.

I did and with 23K+ miles now on the car it does not consume any oil to speak of between changes.

Once you get past the first 1000 to 1500 miles, the engine is broken in, and you can stop worrying about varying RPMs. you can drive it on cruise at 80 for a trip cross country if you want, it won't harm you.

see what i mean?

Picked up my JettaWagon TDI last Thursday and on Friday I used it for work to go for a 350 mile commute. No cruise control, varied the RPMs with the foot for the entire time. No cruise control..

Then I used it Monday to commute from NJ to central VA and back Tuesday night. All with the foot and varying RPM. I actually welcomed the opportunity for Stop and Go traffic because I got to travel in the 1000's and the upper 3000's. I also wasn't afraid to step on it during the last 500 miles a few times. Now I have about 1200 miles on the car (Which never had to downshift for climbing some major hills in VA! With 3 big guys on board)

I finally used the cruise during the last 50 miles last night and it is a real blessing. My right foot was getting sore...

So.
I think you are fine after a careful 1000 miles to use the cruise... In my opinion.

Love my new car