Eh. “ppm” generally means “parts per million.” Hence the confusion.
Yes you ar correct now that I think about it. (Note to self: do not post first thing before caffeine). I think the time is in sec. so what you end up with is a number something like 10E-9 ppm/s. That is one small leak. Hopefully I have not muddied up the waters more. The important thing is that there is no such thing as a perfect seal.