To force the datetime node to re-run you can use the following python code here (Force Run Python - Revit - Dynamo (dynamobim.com)).
Make sure you add this as a new python node!
If you rename any node(eg your original python node) with “*Force” without the quotes of course, it will force that node to be re-run everytime. Though i would always keep the inputs you currently have within it, so it is keeps your original python node running last.