afaik, guessing anything not 00000 or 11111 at first step will lead to an optimum strategy of 3 steps. because you introduce possible "right digit at wrong place" as a third state.

guessing 00000 or 11111 removes that third state and leaves you with simple substitution of wrong cells, which leads to an optimal 2 step strategy.

but obviously the shortest strategy is just guessing it right on the first try :D lol