So is there some kinda of etiquette on how long you have to comment on a post??

Just go for it. Though some perceive it as creepy. I don't get why though.

You can comment whenever you like. I've seen people pull up threads that are well over a year old. The only issues is the OP may not see it or respond. But, it's always fun to see old threads reignited.

Sure ... I get comments from
Posts I made months ago

You can set your own by letting people know in your profile, or get VIP and lock posts after awhile. Some don't care, others do.

I post on anything that interests me, regardless of when it was posted.

you and me have 30 seconds... lets get to know each other :)

I give it up to a day. 2 if its a really good post.