Its very much possible, most people do their cave key at the first day of the event, which is at May 16th during the last rebates. 16 till now have 20 days, which is 20x50 of daily refresh = 1000, its enough to get another rebates if you were smart with using your moon coin. And if we add tmr we could have 1050 which is the exact amount to get the gold essence. Please before you call it as mathematically impossible, try to count it right first.