The underlying fare has restriction code B3, which means it's valid from 09:00. However the 16-25 Railcard has a minimum fare of £12 for travel before 10am on weekdays. Therefore, since the undiscounted fare is under £12, you can't get the Railcard discount unless you travel after 10am. You will note that BR Fares has an asterisk denoting fares to which the minimum fare rule applies.
The 16-25 minimum fare rule doesn't apply during the months of July or August, or to Advance tickets. So you might like to consider the latter; in my experience, Northern Advances are often available on the day. Note that other Railcards have different time restrictions or minimum fare rules - it is all rather a mess!