add timepoints

io/cells.py

@@ -94,6 +94,10 @@ class CellsHDF(Cells):
     def traps(self) -> list:
         return list(set(self["trap"]))
 
+    @property
+    def ntimepoints(self)->int:
+        return cells['timepoint'].max()+1
+
     @property
     def tile_size(self) -> int:
         if self._tile_size is None: