url_to_unxtime currently has no https support.
Maybe we need this. Maybe not. Currently depends on T131, because we it's not clear yet if we still need an https fallback mode. There is no urge to add an https fallback mode for performance reasons, because there were no performance warnings after asking about this on the tor-talk mailing list.
Actually, it's not an either - or - situation. It's not either Tor hidden services or SSL. Some Tor hidden services offer SSL. For reasons why they might do this, see Notes about End-to-end security of Hidden Services.
So https support in url_to_unixtime would still be useful.
But for now, I am only aware of 2 or 3 non-anonymous, trustworthy Tor hidden services that support SSL. Facebook's Tor hidden services which we probably do not want to add to the sdwdate time source pool list. And some self signed ones?
So this is not that important and can maybe be done a lot later. Depending on how the combination of Tor hidden services and SSL evolves. Therefore decreasing priority to low.