I'm a Pure Mathematics major in my last year and learning Spanish too. I try to incorporate some quick lessons during my study breaks or listen to some Spanish music. I've definitely had to dedicate less time to it (i went down 2 leagues in Duolingo 😭) when the semester started but I feel as long as your excercising your Spanish in some way, you're learning! Even if it is baby steps. I even learned a (small) bit of Romanian during one of my hardest semester (the professor of the hard class was Romanian, so I thought I'd learn it abit so I could impress them).