Copy missing relative information from timelib

Summary: Copy over all relatice information from timelib struct, this fixes some of the
special modify modes, including `+1 weekday`.

Fixes #3468

Reviewed By: @JoelMarcey

Differential Revision: D1663384

Signature: t1:1663384:1415255569:cf95e9f81af740e5d235702cb873c10bb27cb5ec