If your test kit is expired, your best bet is to fly blind. To the QT you've already added 15 drops.
The total dosage for a 20g QT would be 76 Drops.
You need another 61 drops. All at once. Velvet works too quick to wait 48 hours.
With no viable test kit to track the levels properly, pull the live rock. Keep an eye on the ammonia levels and if you need to do water changes, dose the appropriate amount of copper to the new water before you put it in the tank.
Order a new test kit and when you get it you can find out where you are. Even if you're not exactly at the right level in the mean time, the close-ish dose should at least suppress the disease until you know.
Start your 14 day count when you have a confirmed test result.
Don't put the rock from the QT in the display!
Get the mandarin out of the display also. You may want another thread specific on how to manage a mandarin in quarantine, as it may need supplemental feeding, but I really have no idea on the effect of copper on pods, they may not survive copper in the quarantine tank.