Date fields just don’t know about each-other so it’s not possible to have such a validation. One approach could be using an UI extension for this, so the extension would have to be aware of the other field, do the validation, and notify the user.
Additionally, curious how one might handle recurring dates in Contentful.
You mean like an event that is happening e.g. every week on a Monday? or an event that happens on two or more specific dates? I guess you could use the
Object (json ) field type to model something. Alternatively you could model something using the
Array<Link> field type and link to entries of a content type created specifically for this. E.g. each linked entry could represent one date or day of the week.