This has worked on my S7:
Turned off "do not disturb" settings.
Set "switch to mobile data" in WiFi settings to aggressive mode.
Turned on "keep mobile data turned on" in developer options.
If you want instant notificaitons I think an Apple product will work well. All of my Android devices are delayed, Samsung(S7 & S9) and Chuwi tablet but not my Ipad. I just bought my S9 knowing this but using ADB command to disable "doze" and "deep idle" helps get the notifications fairly quick. I think it is an Android issue that started with Nougat upgrade.
Disabling doze was working for me, but not anymore. Don't know what to do. I read all of the articles and forum posts on the internet, tried all of the methods, did 1000 factory resets and nothing. I'm getting desperate. Samsung, Google, Android team... I'm beggin' you guys, do something.
I have the same issue. I love having updated scores but last night I got a whole hockey game in 2 mins of notifications after waking up my phone. I thought it had gotten better, but it hasnt.