[onion2k]

The collective amount of hours wasted clicking those popups must be enormous.

You can't add them up and use that time though. That time is always going to be fragmented in to unusable bits. Millions of people wasting 2s each is not equivalent to thousands of hours of lost productivity. Likewise, one person wasting 2s many of times a year can't be replaced with a useful hour.

The 'lost time' argument doesn't make sense.

[cinntaile]

It's not just the 2s, it's also the frustration wasting time on something that adds no value at all. On its own this might not matter, but many of these small actions (not necessarily cookie related) do affect your productivity because they affect your mood.

[Aerroon]

But they're not unusable bits of time. That 2 seconds you spend would be 2 seconds sooner that you would be done with the website. If you visit 100 websites in a session then that does add up to 200 seconds wasted in that session.