Do you mean you have a product page that has a lot of things that needs to load on the page and you want to know how long the page takes to load with all the bit?
Or do you mean you have a product page that can load one of 1000 different products and you want know on average how long it takes to load the page?
When you look at the attributes available in insights for the page request do you have an attribute the represents the value of the item being represented on the page? Like a product ID? Or does your product page URL contain the product ID in some way?
If you can literally show a URL pattern for a few products and state the unique attributes you might have I can show you how. The other things you say above are useful, but this is a technical question.
Your ex above is not enough to work out the result.
It would be a good idea to also validate the timings and compare pageview duration and webAppDuration to determine which measurement meets your specific needs. They are different and can both be valuable. Also, adding instrumentation to add attributes to pageView will help. Using like can be a problem with complex url patterns. Attributes for product id’s etc can really help long term.