>Aside from that, I expect 40 hours of "quality" braintime from you, and I don't really care where or when those hours occur, as long as you're collaborating with the team when they need you.
There is no way you are getting 40 hours of "quality brain time" from anyone. If you believe you are, you don't know what "quality brain time" is.
Assign the amount of work you feel is reasonable. Let the worker do the work. If the work gets done, it doesn't matter how much time it took. Knowledge workers sell their knowledge to help you accomplish a designated task, not their time.
How much work really gets done in a 40-hour work week? Anyone who has been in any office environment knows that probably at least 50% of that time is always just farting around trying to rack up butt-in-chair time. Consider also that promotions and political favors are usually withheld from people who do the "bare minimum" of 40 hours and that butt-in-chair time comprises 95% of an external entity's (like, say, your boss's boss) assessment of job performance, and the time constraints can become quite demanding.
We should do away with the Industrial-era culture of minutely managing hours (when time working was directly correlated to the quantity of products a company could assemble, and thus counting time allowed the company to reasonably reliably assign a portion of the revenue to its employees) and embrace the Information-era mandate of small, irregular work units moving the majority of the product.
We should accommodate workers such that they can cultivate a fruitful and creative mental state for use in employment when inspiration and flow is most likely to strike (which, for coders, is usually in the middle of the night when there is a solid block of 5-6 hours with 0 interruptions), instead of forcing our supposedly-revered knowledge workers into deadened, drooling blobs stuck to their chairs for 55 hours a week because they're vying for a promotion next year.
It's a major pet peeve to see someone treating knowledge workers like assembly linemen. More butt-in-chair time != more productivity, and in fact, once a certain threshold is reached (probably ~20 hours), it becomes counterproductive.