The idea of concurrent timeline in different story lines is often used in the science fiction world. Robert Heinlein is one writer that comes to mind (mainly because he perhaps my favorite.) I know that he had a huge chart in his office on which were kept the times for his various story lines. Very often his characters would overlap and sometimes even show up in different story lines as minor or incidental characters. It can be very interesting when story lines intersect, especially if you have a dedicated reader base who follows characters and story lines.

The down side is it adds to the complexity of keeping time lines in order and not introducing problems. Readers will spot such conundrums and they will become a nuisance. Too many of them and you can ruin what would otherwise be a great story due to the contradictions it can introduce which can affect the believability of the whole concept.

I timeline but not until I have an almost complete manuscript mainly because doing the timeline while doing revisions just gets to complicated and time consuming. WHen I have a manuscript that has gone through a couple of proof reads and most of the revisions are done, I will timeline it. I can then fix any problems with the timelines for the characters at that time.

For me, the creative part of the writing is the easy part. The stuff that goes on after the story is finished is where the real work begins. Editing, proofreading, timelining, are all necessary evils to produce a first rate work that people will read and enjoy.