It seems to me they forgot to update their text a few years ago when the rule about using night trains changed. For Interrail/Eurail, you need to fill out the date of departure.

[For FIP coupons, this text has always been incorrect BTW.]

Aha, yes that might be so; I didn’t realise this was a recent change. Thank you!

I think their statement might be correct if you get the train from Edinburgh or Glasgow though; Eurail’s mobile pass travel day page states 

For mobile Passes a travel day lasts from 00:00 (midnight) to 23:59 Central European Time (CET). Please note that some European countries do not observe CET. Finland, Estonia, Latvia, Lithuania, Romania, Bulgaria and Greece are all one hour ahead (CET+1). This means there can be a difference in the start and end time of a travel day when compared to your local time while travelling.

So a 23:40 departure from Glasgow would be 00:40 CET according to the pass I presume, even though the UK is not mentioned here.  Confusing! 

Thanks, I didn't know this. Totally weird and confusing. It reeks of changing the rules because of a technical problem.

I found this thread while trying to figure this out (after reading the statement on the Caledonian Sleeper website). I’ll contact the Interrail customer support to get to the bottom of the story - the staff onboard of the train did look at the date of the pass… (which was set to the day of departure).

EDIT: I contacted the Caledonian Sleeper customer service and here’s their answer

The date on the pass must be dated for arrival, but the room supplement would be bought for the date you leave the station - they don't have to have the same date Britrail / Inter-Rail / Eurail / FIP Coupons will need to be valid on the date you arrive in your destination but not necessarily on the date you join the train for departures before midnight.

It looks like it’s not even related to the timezone issue. Next step is to make sure this is mentioned on the Interrail website, I guess?

EDIT2: more information that seems to explain why they chose this (to be more customer friendly)

We wouldn't challenge a pass using the date of travel - for many passengers this is the not the first train they use that day! It's really to help you use the passes 'economically' and not waste one if our train is the only one you're travelling on that day. Some passes give you a limited number of train days in a month e.g. 10 days within a month

This looks very much like outdated information. @Nanja, I suppose Caledonian Sleeper should update their website?

@rvdborgt I'm not so sure, I had a conversation with their customer support about it that I added as EDITs. Anyways, there's not much more I can do about it!

Hi both, I will have it checked by the relevant department and will get back to you once I know more. 

Hi, Unfortunately the rules in Britain for a night sleeper are that your ticket needs to be valid on the day of arrival and is thus an exception to our regular rule for night trains. That will not change despite the fact that we have tried many times. I hope this clarifies the situation. Cheers,

Interesting. This does mean though that the app activates the incorrect day for sleeper trains in Great Britain. I just tested this: it activates the day of departure. Also, the page that explains the travel day does not explain this exception for Great Britain. So many Interrail/Eurail users will probably not know about this and even if they do, they won't be able to activate the day of arrival if they have a mobile pass.

@Marion How should this be handled?

hi, @Marion  do you have any further information on this? I will be traveling on Friday and can't get the app to accept the correct day.

Marion is no longer a Eurail representative but this issue still exists with the mobile pass not conforming to the same rule as the UK sleepers, I have posted a reply in your other topic on this subject.