There’s a time limit, usually set by culture. Too short or too long is considered weird, creepy, rude, even threatening.
I never get the timing right. I try to read the other person’s expectations but it’s hard as I’m not good at face reading but with practice I’ve gotten better.
I don’t care for the feel of a stare but it depends. Kids, dogs, cats, don’t bother me in the least. But most adult staring does, if it’s blank. If they’ve got a question on their face, I’ll turn and ask.
When on Vine, I made use of my eyes to “talk” a lot. It was fun, but I couldn’t do this in person.