Do you experience these time splits and slips in LD's, or NLD's, Dreammouse?

The reason I ask is that NLD's tend to be remembered differently -- and much more hazily -- than LD's. LD's are recorded in short-term memory like any other interesting conscious event might be, so you can have, upon waking, a decent record of where you were during the dream. But NLD's are generally not stored at all, so their record tends to be whatever you could manage to recover upon waking.... and that recovery can be haphazard at best, even if you think you're remembering everything clearly (also, when remembering NLD's you might tend to "fill in the blanks" with things that make the story work, but might never have happened at all in the dream, which is pretty common but I don't think matters here). So, if you were not lucid, there is a chance that the contents of several dreams that occurred independently and in their own time might have been jumbled together and -- in your mind's effort to make sense of it all -- were sort of "layered" on top of each other, giving the impression that you were moving back and forth among several dreams, all at once.

I've had this experience of "layering" many times with NLD's, and would describe the experience itself pretty much the same way you did. However, I have also had more than a few LD's where two or more separate dream plots were unfolding at the same time. I only experienced one plot at a time, but I knew during the dream that another plot was unfolding, and could move to it simply by adjusting my attention, and when I arrived its plot would have progressed, implying things had happened while I was away. I'm not sure this is the same as what you are describing, but it seems similar. The difference may be that, perception-wise, there was only one dream at a time going on, and I never watched, say, a split screen of two or more dreams happening at once (though it wasn't for trying: whenever I attempted this, the two plots -- the splits -- would inevitably and instantly link up into a single stream of imagery.

Also, in full disclosure, I really think that we only dream one thing at a time, and tend to experience them in the same linear manner that we do in waking-life. However, I've also said more than once that time does not exist, especially in dreams, so there is certainly a chance that whay you are describing could really be happening... how's that for ambiguity?!

So: if these were NLD's there may be another explanation beside stepping outside of time to explain what happened, Sure, it's a more mundane explanation, but one worth considering.