Timeline, What Timeline? indicates that the story will not bother with the niceties of sticking to the Gundam Wing timeline (49 episodes plus the OVA 'Endless Waltz', along with the handful of official mangas -the Episode Zero and Blind Target mangas-)
timeline? What timeline? These stories deal with altered timelines. For example, a story in this genre might take an event that happened in the future and place it in the past, change a character's age, height, opinion of certain things, etc. However, these type of stories might not follow any set order of events at all.