so far, we decided not to track PageLoadTimes in our Angular application since we don't get the resources for implementation.
as a possible solution you need at least 2 timestams:
1) user clicks on a link
2) application/browser finished updating the page
so basically your devs need to save a timestamp when user clicks on any link (and save locally). the second timestamp needs to be saved when browser either received data or updated the page. the difference of those timestamps should be added to the dataLayer together with all page information.