I noticed that and I added it. The last issue was my multi-geometries that I had to change into single geometries.

ok,that works halfway: now the point data are showing up, but the clustering functions is not working.

Do you need the solution to be compatible with your actual visualization or are you looking for a possible separate web map client? I used leaflet and a plugin to do something similar (Plugin "TimeSlider")

Well, I have not clear out the theory part of my question, but for the implementation, I found an alternative: I inserted a variable to count multiparts geometries in the first example, and at the end of the loop, if the variable is higher than 0, I call the function Multiparts to Singleparts.