A few things:
Generally I don't believe this will be added to vanilla. This is not a value judgement from me on whether or not I believe it should be in there, I'm just looking at the evidence. There were multiple ways to slow down time previously, such as opening your journal when you were about to go to sleep. Those methods have quite consistently been patched out when discovered. As such it seems clear to me that the management of time as a limited resource is seen by CA as one of the defining hallmarks of the game archetype, and I don't see it as likely that a way to slow down time will be added.
That being said, there are mods out there which achieve this. Such as for example this one, if you're playing on a platform which supports mods.
Control the flow of time in the game: speed it up, slow it down, or freeze it altogether. This can happen automatically or when you press a key in the game.
www.nexusmods.com
Finally, I've played with that mod before. I won't do so again. Primarily because the days by default are a good length in terms of real time spent to finish them. As a forewarning, if you start allowing slow time / freezing time, it was my experience that you very rapidly can acquire everything you want in a season well before a significant portion of the season has passed, and you end up both not wanting to play because the days take too long to complete and not wanting to play because you have nothing you're excited to do. Which is ironic since you can always just go to sleep, but nonetheless, that was my experience. So if you do go for something like this mod, personally I'd recommend approaching it with a wary eye and the foreknowledge that it may well ruin whatever save you play it on and your general game experience.
Regardless, I hope that helps at least somewhat, and best of luck!