The phrase "same timeline" means that two or more things are happening or occurring at the same time. It indicates that events or actions are taking place concurrently and not at different points in time. Full definition
Same timeline as always: whenever it's finished and everybody is ready for that next BIG transition. (theletteredcottage.net)
No two children follow the exact same timeline when it comes to learning to talk. (babycenter.com)
The film will take place prior to the events of A New Hope — somewhat same timeline as Rogue One — and follow Han Solo roughly from the years of 18 - 24 as he becomes «the smuggler, thief, and scoundrel whom Luke Skywalker and Obi - Wan Kenobi first encountered in the cantina at Mos Eisley in A New Hope.» (allgeektome.net)