It has to be something in NL localisation as EN version works well on your frontend.

Possible....i have more problems with translation now....i see that some parts are not being translated, even when i have the language file in place.

Later i will compare the 2 files and align it to the EN-GB file.

Missing translations will be problem of new version, because we do not update other languages. Those language files are created by our customers.

But to your main problem (functionality): It is definitely caused by date format. If you tried to modify language file for NL and it didn't help you, check also configuration (tab General). There can be also date formats which can overwrite language files. Important is DATE_FORMAT_NORMAL (Standard Date Format in Configuration) where if you use "d-m-Y", it would repair all bugs with dates.

It is not final solution and I hope, our development team will solve this problem definitely. But it would help you for this moment.

One more thing, you use hourly reservations. Try to use also this row:
DATE_FORMAT_LONG="d-m-Y H:i"

Tested and it helped me with the problem.

Fixed for now, would indeed be better to fix this in the next version.
Thanks so far!

Of course we will try to solve the problem so you will be able to use any date format.
But new version will be probably realeased later (probably after 2 - 3 weeks).