You should be able to use the EIN immediately and for filing the Forms 1099-Misc for 2019 if the business was in operation during 2019.
When you apply for the EIN on the IRS website, the SS-4 application ask for the starting date of the business. If you're started a new business, enter the start date of the business. If the business you acquired is already operating, enter the date you acquired the business.
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