However, we don't need a perfect measurement, just a reasonable one. For example, you might try to wait for all stylesheets to have loaded, and then run reques

However, we don't need a perfect measurement, just a reasonable one. For example, you might try to wait for all stylesheets to have loaded, and then run requestAnimationFrame until the latency is below some threshold (say, 100ms) to represent a somewhat-loaded-and-not-too-laggy page. The point is, you want some measure that plausibly excludes ad-related resources since clearly you don't care how long it takes to load those. It'd also be polite to be transparent about the limitations of your measure.