Hi Jen, have you always sent the the emails at the same time/day and to the same audience criteria? It could potentially be the processing load in your instance at that moment (e.g. if there are other emails sending or trigger/batch campaigns processing) or possibly even the data center your instance is on. You might want to try using the Head Start setting to pre-process the audience, which may help the send go faster and more in line with your selected time. Generally, I've found that emails can take 24 hrs to deliver, especially to folks overseas. Hope this helps!
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