I'd recommend this tutorial (https://www.learneroo.com/modules/11) and once you're comfortable with the basics of Java, then research some basic mod tutorials
Don't make effect ID static! You don't even need it. Just create a new instance of the enchantment (in the main mod class) and use that instance's effectId, as it is already a field in Enchantment.class.
To expand on Ben's explanation, you will always register the recipe. Whether or not the recipe is called depends on the day.
See here for how to get the month and day.