@Leoooob the problem is that we store a combined timezone so that the timezone list isn’t huuuge. In the case of (GMT +0:00) Dublin, Edinburgh, London we store the timezone as Europe/Dublin which is the same as GMT+1, or BST, as we’re currently in here. Unfortunately this has the unwanted side-effect of making the timezone display in the date/time picker show IST which is the abbreviation for Irish Standard Time.
To be clear, the times are all correct so you can carry on as normal, the only thing that is “wrong” is the abbreviation display in the time field.