There’s no specific number that it “should be”. The base maps are dyno tested, if that is where the vtec engagement window is, leave it as is. Being that you’re a beginner, don’t mess with anything. It’s not as simple as just changing the engagement window, you’ll need to make changes to the fuel maps as well, and possibly to the ignition maps. If you’re interested in learning, there’s several old threads on here that will give you an idea on how to tune. Realistically, fuel is the only thing you should be changing if you’re street tuning.