Add lease recipe.

This is in production at Spotify for monitoring scripts.
I think you have a valid theoretical point, but I'm not sure it is practical.  IIUC, the advantage of using zk node time would be to handle scenarios when client clocks are widely out of sync.  It is rare these days, since machines typically have NTP enabled by default, and if you are out of sync by minutes, you usually have worse trouble anyway. :-)

The disadvantages would be more complex code, and complex testing.  I cannot think of an efficient way to test such a setup.  Does zk provide remote controlled mock clock behaviour?  Even if it does, it would become quite messy.

I should document the assumption that clocks are in sync, though.  Will do.