if you, like me, are really into new year's goals/resolutions/etc but find it (quite naturally) difficult to change a bunch of your life overnight on january 1, you can just... start now!
there's no rule saying you can't start early! e.g. i have a goal to work out more in the new year and i am starting to train now so that when jan 1 hits, i know my body is at a minimum actually physically capable of exercise and i don't wind up sitting on my ass bc i "can't" work out or bc i literally don't even feel in shape enough to get started (yes, this feeling really does happen to me, and yes, it is super dumb). i've done this kind of thing in years past and you would not believe how insanely helpful it can be
in other words: time is made up— the end of year cutoff is totally arbitrary; you can still amp up your efforts to a higher level on jan 1 to feel that nice/refreshing sense of BIG CHANGE, but it can be useful to give yourself at least a little momentum now to make that new year change easier and less daunting when the time does come.
(and obviously this is not to put pressure on any readers to have or create any resolutions of any kind— i know a lot of folks have distaste for them and i totally get why, it's valid! they work for me though so that's why i'm posting this)