The arrival times can be divided into two sets. The first set are pairs with the same number for minutes

(17:22 19:22) (17:45 20:45) (18:06 : 20:06) (19:08 20:08)

Sine Ron tells Tim he's sure Tim can't tell which one is correct we know that it must be in one of these because the remaining times have unique numbers of minutes.

The remaining times are 17:29 18:28 and 20:45. Tim now knows that the hours part isn't in one of these because of Ron's statement. The only hours part that doesn't appear in the set with non-duplicated minutes is 19

Up til now all Ron knows is the 19 hours so he's still not sure whether its 19:22 or 19:08. Once Tim states that he knows the times Ron is sure that the minutes can't be 45 , 06 or 08 because the Tim would still be uncertain about the answer. Ron now knows the minutes is 22 and the hour is 19.