The system tries to crosspost a failed crosspost up to 5 times, at progressively long wait times. (24 hours being the last delay.) If you haven't gotten a final failure in your inbox yet (the one that says "this is attempt 5/5 and will not be retried" or whatever, I forget the exact error message), the system will keep trying. If you have gotten the final failure, then you'll have to edit the post and re-tick the crosspost box.
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