17. At 6:20:25, a certain electronic watch displays 6:20:25. How many times within the hour from 5:00 to 6:00 does this watch display 5 different digits? $\qquad$ kinds.
【Answer】Solution: According to the problem, the highest digit is 5 in one case;
For the tens place of minutes and seconds, it can only be $0, 1, 2, 3, 4$, and they cannot be the same, so there are $5 \times 4$ $=20$ cases;
For the units place of minutes and seconds, there are $7 \times 6=42$ cases,
Therefore, the conclusion of this problem is: $20 \times 42=840$ (cases).
The answer is: 840.