I have been in this situation and it is horrible. The written task list *should* take priority, but you will make enemies for life if you fail to deal with today's crisis (or ask for written instructions first). When you get involved in the crisis management, you will probably be thanked, but the time spent will be forgotten by the next day. Meanwhile, the incomplete written task list *will* be used against you. The only real solution is a change of manager, though adding the extra task yourself to the written task list the same day does help a bit.