How long does it take a herpes blisters to rupture? can a vaginal bump/pimple in my labia minora have a shallow opening?

Probably not herpes: On moist surfaces like the labia minor, herpes lesions typically break within a few hours; often the blister itself is never seen, just an open sore. On dry surfaces, like the labia major, the blisters may remain intact for a few days. From this information it isn't possible to know whether your bump/pimples is herpes. But a single lesion in a hair-bearing area usually is just a pimple.