Advice needed for completing my PhD thesis. Which timeline should I follow?
This would be easier to advise you if you told us what field, subfield you are working in.  Give us less scoop than needed to identify you, but the extra info will help with sneaking in tailored advice.  Although much will be general, there can be differences from STEM to "bull", from theory to experiment.  Maybe we sneak you a little domain specific advice along with the general.
My advice is to push for the earlier timeline.  You have the work done (or a decent chunk of it). And you have published before.  Worst comes to worst, you have to delay.  However...I wrote my thesis in 10 days (literally, and not how millenials use literally).  And I am far from a genius.  Yeah, there was a lot of cut and paste.  And my advisor was pissed off (dumped it on him along with the committee).  But I had lots of papers done and a job waiting.  I had really checked the box on doing what is needed for the union card and gotten him lots of ride along coauthors.  It worked out.

No reason to make a big tadoo about the thesis.  WORST comes to worse, you just bail later.  But I would put the pressure on yourself.  Go for April.  That is a ginormous amount of time.  In the corporate world (or God knows as a PI), you will be expected to produce huge amounts of content in much less time.  The "dreamy" part of grad school is over.  Buckle down and get that thesis out and sent to your committee and the "ruler lady".  Do a decent job but really at the end of the day...darned thing is pass fail.  What matters are papers.  If you are a bull major, than maybe it becomes a book, but there is time to worry about that later.
Use MORE chapters than the norm (e.g a chapter per paper plus methods, intro, conclusions).  You will still need to do a little work to format and perhaps abstract intro and methods to separate, joint chapters.  But it is much easier to write a thesis with more chapters and ones that mimic your papers (less synthesis).  [Don't let anyone else know...let it be sneaky advice that I share with you.]
If you are not already familiar with Tex, I recommend to avoid that and use whatever you published the paper in (probably Word).  Same applies to complicated templates.  Write how you did your journal articles.  [The techies here will scream, but anyone to the left of CS/Physics/Math will back me up...don't make your thesis the time you learn to type differently.]
Start a computer file with the name "Thesis rev 1".  Hit save.  Go in and add a title (doesn't matter if it changes later) and add the different sections, chapters (doesn't matter if they change).  Now you are ROLLING!  This is so much easier now with computers than in the day when you hired a typist.  Dump your papers (whole stock) into whichever chapter makes sense.  You are really started now.
Make a schedule and follow it.  Mine was painful (chapter a day).  But you can do a little better.  I guess give your advisor intermediate drafts but don't let the old goat discombobulate your flow.  Push, push.  Imagine you were doing this whole thing on your own.  The cynical truth is you are. 




Good luck, peanut.