Yeah, I can see the Gmail not being instant, which doesn't particularly both me, but live notification from food apps have always worked for me. Mind you, most apps know they need a persistent notification for best results with this. It's not like I would never get a WhatsApp on time for example too. There are other apps that give me daily notifications at certain times, they always come through on time too.
**EDIT** Are we sure it has nothing to do with having Gmail open somewhere else? So when I noticed it above, I had Gmail open on my PC, the phone knows it's open in other locations? While having breakfast my PC went to sleep, I just looked at notifications on my phone and there's an email notification from 1 minute ago...