I have a couple of developers on a high performing team that are consistently working overtime (nights, weekends).  I've verified that this self-generated and seems to be based on their interest in cracking the problems involved.  Do I try and discourage this based on the principle of sustainable pace?  My fear is that it will simply drive it underground which doesn't change anything and loses transparency.  The motto from a previous workplace was "you can't control the coding underground" and I think that fits here, but I'm concerned about burnout.  The application in question is new technology and a coding challenge both mathematically and graph ically.  The team is producing wonderfully via what they call 'organized chaos' and I don't want to mess with what's working.

Any ideas?

Gary Williams