Board Thread:Questions and Answers/@comment-38972380-20200125042649/@comment-46948801-20200921171643

This is what I think:

Since Dio had a stand and affected the Joestar family (gave them stands), and he could stop time, Star Platinum was also given the power to stop time. When Dio was alive, he was stopping time and increasing it. This also helped Jotaro increase his stopped time (because 1) he did activate his power to stop time and 2) he increased his stopped time to 5). When Dio died, this means that he can't stop time since he died, therefore he cannot increase stopped time. This makes it a fact that Jotaro cannot increase his stopped time anymore.

Part 4- His stopped time decreased because he didn't use it for 10 years.

Part 6- His stopped time increased back to 5 seconds because he stopped time many times in Part 4.