Given a travel related situation, and given a specific question about the situation, summarize the question into a title

I am buying a train ticket from Paris to Düsseldorf (Thalys). Can I hop off in Köln to spend sometime and then hop on an RE (regional train) on the same day (within half of a day)? Or do I have to buy a separate tickets? I know I cannot board the Thalys again, because it requires a seat reservation.

When going by a train from Paris to Düsseldorf (Thalys), can I hop off in Köln and then hop on again?

After reading UK Citizen flying to US, then Canada, then back to UK - How does this affect Visa Waiver Program? I am wondering: 


If you are in the US, travel to Canada and re-enter your VWP clock didn't reset. This is classic.
There are countries, in particular in Central America where a brief visit does count as a "reset".
So what happens if you go USA-Canada-reset country-Canada-USA? 


Is it possible to reset the VWP time counter by visiting a third country after entering Canada from the US?

For a particular hotel I booked Expedia's Check-in policies section states the following:


  Check-in time starts at 4 PM
  
  If a late check-in is planned, contact this property directly for their late check-in policy.


My question is...  what constitutes a late check-in? My flight is scheduled to arrive at the airport at 8:34pm.


What constitutes a late check-in for a hotel and should I inform them about my late arrival?

