I feel that 5 minutes was reasonable given it wouldn’t be seen by too many people yet.
I am extremely used to typing my comment out and then noticing my many grammar mistakes afterwards.
It’s often that it takes me multiple attempts to fix my comments, especially given how bad Google Keyboard has gotten with autocorrect.
This should be configurable on a per instance basis, so not much point configuring it at all, since most instances will probably use the default.
Maybe you should suggest to the devs to change the default for this setting to 5 minutes.
And yes, I do agree that this having this is actually quite nice, especially for non-native English speakers.
Regarding the keyboard, try using SwiftKey by MS. I tried it, but it has no autocorrect settings (just on/off, that’s it), which doesn’t suit me at all (I use custom settings for autocorrect, just underlining and suggestions after I tap the word/phrase), but maybe you’ll like it better than Gboard.
I had owned SwiftKey Pro from before Microsoft bought it, but wasn’t happy with it as it felt like it didn’t get any updates.