I've accepted a few of the XP brews rewards from the current events running both the dungeon divers event as well as the champion training event and none of them have been added to my total XP boost time.   in addition my wife has also received a few of those rewards and her time is still 0 and does not have any XP boost even though she's accepted several brews.   her problem is easier to see because she has zero and nothing has been added to it, mine just shows the same amount of time remaining even after accepting the rewards from the event. 

Hello, I am not sure of your issue. XP brews are used to lvl champions without using energy to farm the xp. If you give a champ a xp brew the level will raise. The more brews you give the champ the higher the champs level will go until he is maxed.