I would like to have the option to limit my smart list to an estimated time of eight hours. Something like this:

"totalTimeEstimate:'8 hours' AND (list:ProjectA OR ProjectB) AND location:WorkOffice"

for tasks that can be done on either project A or project B in the work office, with a maximum total of eight hours worth of tasks.

A possible use case would be to be able to see which tasks you will be able to handle before leaving work for the day.