WebPagetest Forums

I want to only collect data for certain set of domains albeit the page have multiple other domains. Is there a way I can select a subset of the domains in a clever script/block or some other way to calculate this time?

My motivation is to demarcate the time between first and third party for some arbitrary definition of third party

If you use the API you will get the timings for all of the individual requests. Then you can do whatever you'd like to calculate the separate timings. Be aware that the high concurrency of browsers mmeans that not all requests are on the critical path so even if a 3rd-party request takes a long time it may not have any impact on the page at all.