Information speech web Performance Speech

Hi,

First of all I would like to thank you for your speech about Web Performance (link here : https://www.youtube.com/watch?v=6Ljq-Jn-EgU ) because it is really well done and unfortunately it is difficult to find information about real world tests concerning the metrics of an app speed.
I am working on a project where I would like to measure, for each user of our own internal apps, how long does the user wait between the moment he sends a request (whether it is by clicking on a link, making a research thanks to a search bar,...) and the moment the page is interactive, and he can use it to send another request for example.
By the way, your speech and research interest me a lot because I am really focusing on real world measurement. Unfortunately, I have difficulties to understand which properties correspond to the ones I am interested to. Indeed, I don't want to select the number of long tasks, but I really want to measure all the time spent between the moment the client interacts with the page and the moment he can use it again, whether it is an Ajax request or not.
I was studying Performance Timing API, and Resource Timing API, but Polyfill seems to be a great tool too.
So, maybe you have an idea of which time marks are the one interesting ?

Looking forward to hearing from you,
Thanks again,