When Blackout Dates are created, they are done so in UTC. So if you select 9/7 as the blackout date, then you are saying a start time of 9/7 at 0:00 UTC and end date of 9/7 23:59 UTC. See below.
In CDT time, this would be a start time of 9/6 at 7:00 pm and end time of 9/7 at 6:59 pm. So if a campaign is scheduled after 9/7 at 7:00 pm, the campaign will not have an On Hold status or see the warning message as seen in the linked article above.
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