Currently the modeshape fedora will request a "Slug" header be supplied to use as the label of the version. This should be taken out, to be replaced by the Memento-Datetime header, if that's present. The label should be a timestamp per the Memento DateTime Section of the Memento spec: c.f. https://tools.ietf.org/html/rfc7089#section-2.1.1 .
If an invalid Memento-Datetime value is set in the header, a 400 should be returned.