My general rule is no posts or replies for a month. I figure at that point it’s clear that nostr isn’t really a priority for them. With very few exceptions, I want to follow users who are consistently active. And very large follow lists seem to cause problems with user experience, so me following an inactive npub is essentially like dragging around dead weight from relay to relay. 

But I also make exceptions to my 1 month rule, such as if I know we never engage with each other, or if they’re a little bitch ass hoe, etc.