I had a company reach out to me today that wanted help with a promotion that they were starting today for today. Tag you read that correctly that they were launching a promotion today for today. CRAZY!!!!!!
Overall this idea is bad. For Halloween you see the stores start promoting in September, yeah you might be doing a super special sale on a holiday but start letting potential customers know about it farther in advance. Promoting on social media days to a few weeks early will help. If you want to promote heavily on one day that is okay. Keep in mind you might not get the result level you were hoping for.
The value of publishing content early is huge. The issue is that with any holidays is that you want to get the content out 4-6 weeks before the event. Then you can spend the time promoting the event and growing the recognition of the new event.
In conclusion do not wait till day of to promote anything ever as you want to build a following and spread word of the event.