While trial projects are actually useful things that need doing, I'd hazard a guess based on my experience that the majority of trial projects never actually launch. Some do. Some get passed off to the person after hire to further polish, and others go to another team to review and tweak and evaluate shipping.

I can say that the trial I did nearly three years ago took me 3 weeks to do, and I put 6h30m in the first week, 8h in the second week, and 6h45m in the third week, for a total of 21h15m.

Also, just to be clear, everyone gets the standard $25/h rate, it doesn't matter if you're a developer from San Francisco or customer support from the Czech Republic. It's something that's easier to standardize, is typically for a short period of time, and has zero correlation to final pay -- which is normally above market rates for wherever you happen to live.

I took a ~4% pay cut when I came aboard at Automattic, which was more than offset by company paid benefits (Health, Dental, Vision, Life Insurance all company paid at 100%, I just took 12 weeks paid paternity leave, 401k matching, work trips and conferences are 100% expense-able, etc), and got more than that raised back on my first year's annual salary review.

Source: I've worked for Automattic since May 2013. It's a great place to be.