Talking to some of my (to be honest, male) classmates, it seems that a lot of their partners have a hard time with the fact that they can't always talk when they want to, which is why sometimes a set plan is best.
Dating a fourth year med student
So for a bit of my own background: I dated a guy for 5.5 years, with 3.5 of those years spent with him in medical school.
We went through the whole process of applying, starting, doing the pre-clinical years, and all of his third year together.
I know there's one girl in my class who has a standing 6 PM phone call with her boyfriend who lives several states away - it's right when he gets home from work, and right before she goes to the library.
It carves out that little bit of the day for their relationship, and something that both partners know is a part of their day.
That being said, as focused as you are during a study session, everyone needs to take a few minutes to just take a break.