It's possible for painless blisters on the penis to go away quickly within a day, but it doesn't necessarily mean they were due to herpes. Herpes lesions typically take some time to resolve completely and may recur in cycles of outbreaks. To determine if these blisters were related to herpes or another condition, it would be best to consult with a healthcare provider who can provide an accurate diagnosis through physical examination or testing if needed. If you have any concerns about sexually transmitted infections like herpes, getting tested is always recommended for peace of mind and appropriate treatment if necessary.