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Yeh, same for me. First couple of submits timed out, then eventually came in just under 12s.
CW code runner servers were choking badly yesterday, so everyone is experiencing the same problem, not just this kata ;-)
It seems like whether the solution passes or not may depend on server load...
I just couldn't make it less than 15s yesterday and the exactly same solution passed today morning. (in utc+8 time)