Good game, some issues with incremental desync, but nothing serious. The concept is great as a frame, I think you could have done a lot with the portals. I actually quite liked the section where you just locked one of them up so you could play the level. I already found it to be quite frustrating at times, especially around splitting focus, even without there being the sorts of choices that would make it more engaging.
The single long map was fun, but I feel like this could have benefited level design wise from a level system where you have all four directions available to you, and you can do different set up pieces, maybe even play around with horizontal or vertical alignment (or both in a level.) Maybe some interaction or shared spaces, and/or more places to sync up, that sort of thing.
I cleared it as well, the music loop was quite good. The ticking was very recognizable, and quite thematic for a timer. The blue and red divides did help make it quite readable, particularly important because the stages were so large. I wonder if you could have significantly nerfed jump height and fall speed, and gotten something similar done in a more compact (and easy to read) space.
I still had quite a lot of fun with this, there were some nice puzzley elements, even if the whole experience was quite tense.