Changing from IT/Chrome/Miles won't affect your graduation date.
Cards that graduate tend to grow just as well as the ones that start out unsecured.
not sure what you're asking here.
If discover allowed you to convert your Discover It Chrome secured to a Discover It secured, then yes it's still a secured card that just falls under a different rewards structure. Now if they allowed you to convert your discover it chrome secured to a Discover it unsecured, then they should refund your deposit.
As for whether you wait to close a secured card until it becomes unsecured, I'd have to state that it doesn't really matter. Closing accounts have little affect on your credit unless you have high utilization. So whne you close it doewsn't really matter because regardless if you wait or not you'll get back your deposit
Hope this helps!
You can close a secured card at any time. Not sure if discover takes any balances out of your security deposit or allows you to pif and just send you the whole thing.