sorry I did not phrase that very well, when I said as a general rule I believe I meant that if put to the test it could be often won on length alone in conjunction with the activity being done, but almost always these contracts are substantively unconsionable and of course people contest that, because most people don't get angry and want to fight for no reason, they do it because it is violating their rights.

As an example I have an email account with site A. I go to site A and log in, they suddenly spring a large new contract for me to read, I cannot get through to do what I came to do, it will take me 5 minutes to read so I click OK because I am on my way to check my email with site A. Procedurally this is not reasonable behavior.

What would be reasonable?

"Hi, we are changing our terms of service, you can see it at this link and agree. If you don't have the time right now you can do it later, but in three days you will lose access to the service unless you agree to terms."

There are however lots of other laws in the EU which may in fact make this behavior substantively unconscionable anyway. I certainly believe there would also be substantive arguments to be made in this case.