6mins should be fine and usually the trains wait for each other :) 

Note that for the Villach - Venice train a surcharge will aplly (10€ in 2nd Class) you can pay it at a Austrian Ticketoffice for example Salzburg or even on the train 

Okay thanks for your answer, but why the 10€ surcharge is not mentioned in the price on the interrail ticket ? It show that we have to pay only 2€ For villach to Venise 

Don't know the surcharge applies since few years on the Railjets and Eurocitys from Austria to Italy i can only provide a German Italian Page about this :/ OBB Italiapage about surcharge

Not sure where you're seeing a 2 EUR fee but the rail planner app is misleading in stating that a reservation is required from Villach to Venice. It is not. However, there is a 10 EUR supplement, which the app doesn't mention. You can also buy this supplement via the ÖBB website if you indicate you have an Interrail.

@Nanja, this is something that should be improved in the rail planner app: if it says "reservation required”, people will buy a 3 EUR reservation (which is not required for this train) and then be forced to buy the supplement (which IS required for this train) from the train staff, possibly with an extra fee for buying it on the train. The same is true for the EC trains München - Bologna.

@rvdborgt the surcharge is the same on the train without any extra fee

I was sometimes lucky that the staff didn't charged this fee

Okay so we have to pay 10€ on the train or in the obb website ? What is better, to pay in the train or on the website ? And if we just show our ticket villach venise ? (Because we had a ticket after paid the 2€ fee) maybe we will not have to pay the 10€ surcharge ? 

I'm not sure what you mean by your ticket Villach - Venice for a 2 € fee:

1. Your Interrail is your ticket.
2. Did you maybe pay for a reservation (2€ is quite cheap though)? What does it say? Where did you buy it?