The semester has just wrapped up. This means that for the next several weeks, the campus will be blissfully vacant. Yes, there will be a few students wondering around for summer school. As a grad student, this is most likely the busiest time of the year. We finally have long stretches of time without interruption from courses or teaching. Finally, we can get to the field for collections, observations, and experiments. Finally, evenings will be spent writing instead of grading lab reports. You can devote entire days to working in the lab and running analyses.
Of course, all of that is true unless you're teaching a class to earn some money. Are you traveling to summer conferences? That's more time spent away from your work. How about taking a short course or traveling to see family? Time and more time. The truth is, summer as a graduate student is really no different than the long semester, except maybe not so fast paced at times, and you're busy, just with different things.
I believe, and have experience with, that expectations of work output during the summer increases as the perception of available time increases. Expectations are the great unspoken elephant in the room. These expectations comes from both you, your advisor, and others in your department. I've experienced very very low and very very high expectations, both spoken and unspoken. You'll find that this ebbs and flows throughout the year and where you are in your grad career. It's important to ask periodically what the expectations are and, most importantly, if you are meeting them. This means being honest with yourself and your advisor.
When is the best time do this? Summer. Both you and your advisor will have a little more breathing room and probably won't feel as rushed as during the semester. Of course, all of this depends on what your research is, where you are in your degree, and you and your advisor's personalities. I firmly believe that one of the best traits a grad student can have is initiative. So step out, suck it up, and ask for clarification and feedback. You'll be surprised what it will do for the relationship, work atmosphere, and productivity. So start summer by setting everything on the table and clearing the air. It will help with your sense of accomplishment and time management.