In the first stage, the velocity of A relative to B is , and the initial displacement of A from B is .
When A is due East of B, its displacement from B is , for some . Considering the change in the component, the time taken for this is hours. In this time, the increase in the component of A's position relative to B is . So its position relative to B is now .
In the interception phase, the velocity of A relative to B is (according to my working, and I think to yours) . Therefore the time A takes to intercept B is:
hours minutesBut check my working, won't you?