Sometime after the release of Sylas.
My guess would be that they'd get released in the middle of febuary or at the beginnign of march, as there'll be likely 1 or 2 patches between the release of sylas(who'll likely be released next week) and the reveal of the VGU(and then we'll get them ~2 weeks after the reveal).
So if Sylas gets released on the 23rd january,then Kayle and Morgana will likely be revealed ~6th or 20th febuary and then be released on either ~20th febuary or ~6th march.
Of course I don't have insight about how well the updates for these 2 are going forward,so depending on how lucky/unlucky we are we might get them 2 weeks earlier/later.
Though given that Riot announced that we won't get a roadmap until their release I'd actually say that "later" seems unlikely.