Now be careful. Put it in your theme’s functions.php and reload your website once. Then remove the function. I insist on loading your website only once, otherwise prices will be added several times and then you’ll need to delete all prices in order to start fresh. So please make a backup of your database before using this.
Replace array( ‘2019-12-20’, ‘2019-12-31’ ) in line 6 with your own dates. You an also set “repeat” to “off” if you want (line 7).
I hope this helps. And sorry it’s a bit far-fetched, I need to add more filters/action hooks to the plugins. I’m also thinking about adding “Global prices” (like the other addons) that will apply to all products. I didn’t want to do it at first because all products can have a different price, but it seems that a lot of people need this feature.