Heya! I noticed that you also asked this question on our discord community. I have already answered the same there, but I'll quote myself,
The best time to publish a video solely depends on how many views you have in the last 28 days or according to the data visible in your analytics. There is definitely a set amount of views that you need to get in a month to unlock that; however, there's yet to be a concrete answer as to how much. As you have said that you have had it unlocked until now, it means you have met the qualification to unlock it. You need to ensure you get a good amount of views for YouTube to analyze your channel and suggest the best time to publish.
TubeBuddy extracts the data from YouTube and suggests a chart you can use. However, if there is insufficient data from YouTube's end, we won't be able to extract it either; thus, you won't see the best time to publish the table.
Hope this helps.