It really doesn’t take long to grind a tsp of cumin, and the seeds stay fresh so much longer than the powder. And if the seeds start to lose their punch just toast 'em.
Get a bigger mortar then you think too. You’ll read about making pesto, or guac, or lots of Thai dishes, and wonder if it real does taste better. Sadly it does and you’ll regret your small mortar every time you make guacamole.