Well technically, premium kicks in around the 4:45 mark.
Why? Because whenever the battle ends, the "You have been defeated" or "Congratulations, you have won the battle" notification remains on screen for around 15 secs if you don't click on the "OK" button yet.
So even if the battle ends at 4:43, simply do nothing when the end game screen appears, and the time it remains there will take you past the 4:30 mark and give you the premium.
I noticed this around 2006 right after it went retail. And again during the last event when I got wins added to my counter.
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