I too miss this option in the new V3 app.
I understand this won’t work for everyone, but there is a paid third-party app, sharptools, which has a rules engine that can handle the following situations
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send a notification if a sensor is left open for 10 minutes
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send a notification if sensor is open at 10 PM
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send a notification if a sensor is left open for 10 minutes after 10 PM
There is a free trial and then different paid tiers depending on how much you want to set up.
It works for those using the V3 app, including those who never had the classic app. And the rules engine is browser-based, so there’s no android/iOS issue if that’s all you need. 
I don’t want to hijack this thread with further discussion, but if you have any other questions about sharptools, see the following thread (the topic title is a clickable link)
Again, I would rather see it added to the official features in smartthings, but there is an alternative if you are willing to pay for it. You may even find that the free features give you everything you need, although that will vary from person to person.