Homework Policy for Advanced/Honors Students
My students are already slammed with homework, so when possible, I try not to add to their misery.  I have done some formal polling of my students several years back, so I have used real data to balance my own approach.  Of course, as of this writing, I cannot find those numbers any more, so I will be working from rough memory here:

I mentally aim for 50% of the kids to be able to finish labs during provided lab time. In reality, it is usually closer to 15-20% of the kids who are able to finish the labs during the provided lab periods, but there remains a large portion are able to complete their work in &lt;3 hours of outside work (something like 60%).  Only the remaining 20-25% had substantial work from the labs.  While I offer help outside of class, I have not found a reasonable way to prevent this problem; kids who are slow at labs will always take more time than I can provide.

If I am teaching a brand-new course with a brand-new curriculum, all bets are off, as I have very little sense of how long the activities will take.  

However, I once found a Williams College professor's labs posted online, and she added a short question to the end of every lab to the effect of, "How long did this portion of the lab take you?  This answer will have no bearing on your grade, it is only used to help me adjust student workloads in future years."