Tracking time on a project

I have a very large, very detailed project that I am working on and there are a few things I have sent to 3rd party vendors I’m looking to bring in-house. One of those things is tracking time spent on a task. I’m looking for a way to track when a user opens a task to the time they close it. I can’t rely on modified date because I have power automate flows that update these tickets throughout the day and I can’t rely on a user “hitting a button” to start the time. I need a method to track when a user opens a ticket and then closes it automatically. Question is how do I do this?

Basically “Jane Smith” gets a request to work on a project for “XYZ Corp”, each time she opens the task I need to track the time … to the second. Then, at the end of the month, I generate a bill to be sent to XYZ Corp. At the end of the month the time is calculated, saved and then reset for the next month.

I’ve got to do this in SharePoint. I don’t mind grabbing an app to do this as long as it ties into the list I have.

Any suggestions?