You can reapply whenever you're ready, however it will likely take a bit longer to process than the first application because they will need to look into the reason for the refusal and check whether you now meet the requirements.
They advise not to use priority if you have a refusal because they can't guarantee fast processing, however, it's still likely to be quicker than not using priority because you will still get put to the front of the line... So there's no harm in using it.
As a quick reassurance though, approximately 95-98% of applications made in the US are approved - if you meet the requirements and provided all the documents, there's no reason why it should be refused.
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