How to split temporal sequences to sub-sequences in a meaningful yet unsupervised manner?
It seems like your problem is not a typical "time series" problem: in data science and related problems, we normally look at evenly-spaced time series (that is, a measurement every interval, with each interval being the same length, such as 1 second, 3 months, 24 microseconds, etc).

There exist methods for working with events that can take some random time to happen, see survival analysis. If the coordinate domain (e.g. cell location) is important, you probably need a much more structured statistical model. Either way, it feels like unsupervised learning won't help you much.

Unfortunately, you haven't explained your data format very well. Without a 
good understanding of your $x \rightarrow y$ relationship, nobody will really be able to help you. What is being observed? What do the numbers mean? (Time until the next event?) What groups are you trying to get? (Sequences of cell events?)