When to schedule visits?

[MaeN]

One school invited me for a visit, but I'm picking the date. Does at least one day need to be a weekday? Should both be? Neither? I'm not sure what's typical but I want to make sure I'm taking full advantage of the visit and also limiting the amount of classes I miss this semester for undergrad. 

[TakeruK]

Pick only weekdays. Best to pick a day adjacent to a weekend so you can use that as a travel day (and/or a day to explore the city on your own, if you want) since that minimizes classes you miss. If you visit on a weekend, there will be no one around. Keep in mind that these visits require a lot of admin support and they definitely do not work on weekends. Professors might do some email or work at home on a weekend but they won't be in the building. Also everything will likely be locked. 

It's tough to miss classes but ultimately, you will learn a lot more and get a lot more out of these visits than a class! I would recommend choosing a Thursday and Friday visit. Use Wednesday to travel to the school, visit and Thurs and Friday, then pick a later flight home on Saturday (or Sunday morning) if possible so that you can explore on your own if you wish. Also, choosing to stay for a Friday evening usually makes it more likely that students will do social things with you that night (compared to a Wednesday night or something). But this depends on the culture of the department. For my old department, grad student visits are a huge social event and there's a small committee of students that form to create a fun experience for visitors!

Another strategy is to check the department website and see if there are major events happening on certain days. For example, when is the weekly department seminar? Or, is there a seminar series where grad students present? Attend those days. It gives you a very good feel of what it would be like to be part of that department. Personally, I would pick Thurs/Friday over seminar days because the social events and the interactions with students was a high priority for me in choosing schools since this is a time where you can informally interact with students and get candid and honest answers. However, if that doesn't work, then the seminar days are good too. The caveat is that it's a small sample....all seminar series have hits and misses so if you go on an abnormal week, you won't really know if it's the same every week. But it's better than going on a day without anything.

Finally, your sidebar info says "Planetary Science" and I think the nature of the visit could really depend on the department. I did my PhD in a Planetary Science program that was part of a bigger geological/planetary department rather than an astro/physics one. I noticed that geo/earth science departments tend to have more community events in their visit dates with grad students doing a large part of the planning and there were things for me to do all the way until bedtime, while my astro/physics visits were just the "business hours" and the students might take me to dinner but then that was it. Could just be my limited experience though. Also, one of the geo/earth science departments included a field trip in their visit dates! Might not happen if you're visiting by yourself though.