How about, about 20-50 posts? Somewhere along that line?
I don't see how days would work, someone could just be registered for a bit not posting, and then post links, I dunno. In addition to the post amount perhaps? (If it was needed?) But I can't think of a reasonable amount of days. Not saying that just because I can't think of an amount of days that it therefore won't work, I'm not invoking the Personal Incredulity fallacy
EvF
I don't see how days would work, someone could just be registered for a bit not posting, and then post links, I dunno. In addition to the post amount perhaps? (If it was needed?) But I can't think of a reasonable amount of days. Not saying that just because I can't think of an amount of days that it therefore won't work, I'm not invoking the Personal Incredulity fallacy

EvF