Email is Delivered represents (accurately) when the email was delivered to the first hop from Marketo. If you're talking about subsequent hops,the few outliers could take *days*. An arbitrary wait of 30m doesn't make sense as the average time-to-inbox is going to be under 1m, thus well inside the window for whatever else you were going to do -- even if you were going to send them another email for some reason.
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