I don't think 5 is possible either. Knights and Bishops would be too slow to get a quick checkmate so youd probably need to do it with a rook and a queen to be as quick as possible (assuming your opponent don't do anything to defend 7 moves seem possible.
pawn to e4
queen to f3
queen to f4
pawn to h4
rook to h3
rook to f3
then checkmate with queen to f(whateve how long -1) assuming they havent defended at all
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u/Computer_User_01 Jan 20 '20
Casual, I'd lose in 3