The rail planner app doesn't adhere to the conditions of use and uses local time to determine the end of a travel day. So if you add a train to your pass that departs at 23:45 UTC, then it will book that train on the same day as the train from Edinburgh. You can test that with a future travel date. The app won't ask to activate a new travel day.

There are a few things going on here. According to the conditions of the pass, as you say, it will cost you a new travel day because you’re departing after midnight CET.

The app doesn’t behave that way, and uses local time instead. That doesn’t mean it’s allowed, as such. But it does mean that on this occasion the glitch is in your favour and you’re unlikely to have a problem. 

(You should note that the glitch works the other way sometimes, when you want the train to count tomorrow, but the app says it counts today. Currently there’s a workaround for that, but if and when the glitch is fixed, your journey won’t be possible any more.)

A second potential problem is your route. The outbound travel day is intended for travel from anywhere in the UK to your point of departure (Eurostar, ferry, airport). If you’re taking a roundabout route like this, it’s well outside what is a rational route.

Again, in practice this is unlikely to pose a problem. Any inspection will show you have a valid ticket, and the inspector is unlikely to care about your route. But don’t be surprised if they ask questions. 

There's no rule that says you have to travel via the shortest or fastest or "reasonable” route.

Not a specific rule, but it’s clear that the intention of CoR use is for residents to reach a border in order to travel freely abroad. And that the pass can’t be used ‘extensively in your CoR’.

It wasn't so long ago that we couldn’t use it in the UK or Eurostar at all, and it would be a shame if it was taken away again. The pass is very flexible and easy to use in the UK, and remarkably good value (a single Edinburgh to London journey is ‘worth’ £200).

Trying to get as much value as possible by taking a long way round, or by using it for journeys not connected with departing the country (which people have talked about in the past) can only lead to discontent within RDG and Eurail, and restrictions being placed on its use.

That may be the case, but Eurail themselves loosened that rule a few years ago. Previously, it was formulated much stricter. If they don't want people to take the long way around, then they shouldn't have changed it. Or put differently: there must have been a reason why it was loosened.

OP's profile seems to indicate that they live in Ireland so it wouldn't be an issue here anyway.

Well spotted, apologies to the OP!

In that case, it’s just the CET glitch that the they have to watch out for.

Thanks for all the feedback.

As pointed out, I’m not from the U.K. so the concept of inbound/outbound days doesn’t apply here at all.

On a related point, I have looked at long sail/rail combinations such as Thurso-Fishguard-Rosslare, but while there is a route I think it’s not possible to do it within a single day, even when leaving Thurso on the first train of the day.  I think I can get as far as somewhere in south Wales before everything shuts down for the night and then have to wait for the train to Fishguard in order to get the boat.

While it would probably not cause any problem in practice as I would have a valid point to point ticket, I think the terms officially say that you have to take the boat the same day as the train and this wouldn’t be the case for this trip.

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