Just was adding "Not now" to a notification dialog in my app today simply because it feels softer. But it's a definite "no", the prompt won't appear again unless you enable notifications yourself later from the settings (hence the "now").
That behavior wouldn't be clear to me as a user unless it were spelled out like you just did. My expectation when I see "Not Now" is that there will be a "Sometime Later". I would recommend changing your language here.
