What is the optimal balance of time spent on research vs. volunteering/leadership/organizing in grad school and beyond? In graduate school I have found that along with being a producer of good research, fellowships/post-doctoral advisers/faculty search committee are also often interested in what one has done outside of research (or teaching/TA-ing) as well. Examples of such activities include (but are not limited to) volunteering with younger students in science, organizing a journal club, mentoring undergraduate researchers, etc. In some cases, the importance of these activities is immense: for the NSF CAREER award, for example, having outreach is a substantial part of the application. 

However, clearly, spending all of one's time on these activities is not the best idea, since then no research gets done. 

So, my question is:

What is the optimal fraction/amount of time to spend on "outreach" activities like those mentioned above, which are explicitly not research or teaching activities, for someone looking to pursue a career at a research university?
Short answer: You should spend "some" time on volunteering and leadership activities.

Unlike an undergraduate student, a graduate student is primarily focused on research, so you don't want to spend "a lot" of time elswhere. Even so, proficiency in other activities is something of a "tiebreaker" against another candidate with comparable research activities that doesn't have "outside" activities.

This is in contrast to undergraduate work, where "leadership" is the "whole game" for some students (for later life)--provided they pass their courses.