I was talking about the wrong date in the post title. You can still fix this, Lemmy allows editing post titles (and links).

There is no shame in scheduling posts you were going to make anyway, prominent poster @MentalEdge@sopuli.xyz does it and I do that on my @ChaoticNeutralCzech@lemmy.one account. The easiest way is to write a Python script with the pythorhead library, and automating it with a cron job or Windows’ Task Scheduler, or run manually if you wish to do that. Your username and password, as well as what the previous post was (for unpinning in the community), can be stored in your OS’s environment variables.

In your case, it’s just a matter of something like

# warning: untested
from pythorhead import Lemmy
import datetime
import os

todays_date = datetime.now().strftime("%A %B %d")

post_title = "The Daily Checkin for" + todays_date + " - Just For Today, We Are Not Drinking!"
post_body = "Good morning sober peeps!!\n\nWe may be anonymous strangers on the internet, but we have one thing in common. We may be a world apart, but we’re here together!\n\nWelcome to the 24 hour pledge! I’m pledging myself to not drinking today, and invite you to do the same.\n\nMaybe you’re new to c/stop drinking and have a hard time deciding what to do next. Maybe you’re like me and feel you need a daily commitment or maybe you’ve been sober for a long time and want to inspire others.\n\nIt doesn’t matter if you’re still hung over from a three day bender or been sober for years, if you just woke up or have already completed a sober day. For the next 24 hours, let’s not drink alcohol!"

community_id = 5759 #lemmy.world/c/stopdrinking for lemmy.world users
previous_post = os.getenv("STOPDRINKING_PP")
post = ""

lemmy_username = os.getenv("STOPDRINKING_UN")
lemmy_password = os.getenv("STOPDRINKING_PW")
lemmy = Lemmy("https://lemmy.world") 

def retry_login():
    if not lemmy.log_in(lemmy_username, lemmy_password):
        print("Failed to log in")
        exit(1)

def retry_post():
    global post
    post = lemmy.post(community_id, post_title, body=post_body,)
    if post:
        print(f"Successfully posted ({post['post_view']['post']['ap_id']})")
    else:
        print("Failed to post")
        exit(1)

def retry_refeature():
    global previous_post
    global post
    post.feature(true)
    if (previous_post):
        previous_post.feature(false)
    previous_post = post
    os.environ["STOPDRINKING_PP"] = previous_post

def retry: #this structure allows retrying in the interactive shell
    retry_login()
    retry_post()
    retry_refeature()
    input("Press Enter to exit...")
    os._exit(0)

retry() 

This command makes the script run in interactive mode, so you can see error output if problems happen, change variables and type retry() commands to retry:

py -i stopdrinkingtoday.py

I haven’t tested the code but it should not be too hard to get it working. Feel free to ask for help.