Here's what I would do if I were in your position, if I let them out and then called them and they didn't come right away when called I would leave them out there until they knew that you were playing their came anymore.
Actually that is what I recently started doing more, like yesterday with Tasha. I called and when she didn't come, I just shut the door and started doing my own thing. After a couple minutes she came up and looked in the door wanting to come in, but I let her sit out there a few more minutes. I just hope after a few times they make the connection. :P

Their timing is flawless though, they seem to know just when they have the advantage to push the line.

Most the time they're really good about listening. I just don't want to do anything that actually reinforces the behavior, like Crikit was talking about. In my experience dogs are notorious for making a game out of things like this.