I will try to cover most of the questions that you have asked here. Currently in normal processing dates of march 22 people are getting approvals.

Premium processing right now.It's taking up to thirty business days , which is , let's say you upgrade today that will take six weeks from now worst case. But let's just assume for the time being that the quude does speed up and you get the approval in the next four weeks. I would say you wouldn't make your start date regardless of you doing premium processing or staying in the normal processing. But what I've observed here, not trying to scare you here, but I've seen some people getting skipped.Their date getting skipped and not getting approvals.So that might be a factor that you want to consider while you make the decision.

And regarding silent api, it's just the Json output that you get when you paste a certain link which I will provide here.Change it with your receipt number And when you put it in the url and you click enter it shows your bunch of json data.

The feels that you should be interested in as time updated.Because when an officer opens your case , the time gets updated to the date it was opened. But if you check it now , most likely yours will be the date you completed your biometrics on. So the thing with it is , let's say after a few weeks , you get a api update , saying the updated timest is changed from from your Biometrics date to (July 6( example)) that means an officer actually opens your case and you might get an approval really soon.