Dealing with typing archaic letters to get a specific date/time pattern is just wrong. And a link to a PHP manual is not the answer... unless you're a programmer.

Some options - there should be a list of common examples on that page (e.g. how do I add am/pm) - Replace the PHP.net tutorial link with one on bdcms.org that explains it better - get away from having the user deal with PHP stuff. Provide some kind of drag and drop or GUI to help. Not sure what at the moment.
This always takes me time to figure this out.
Recent comments
@yorkshirepudding, In the end I fixed it by deleting the config/active folder contents, copying the config/staging/ files into config/active, importing the database again and clearing the caches...
Importing the staged config throws an error: another field with the same name already exists
Thanks, I have to go out now, I will try later on and report back
Importing the staged config throws an error: another field with the same name already exists
Hi Francis. Yes, what config do you have in staging for it? You might have configs like: field.field.field_video_embed field.instance.node.page....
Importing the staged config throws an error: another field with the same name already exists