The way my availability works is I am available almost any time at all I just need to be messaged when you are available. So my schedule revolves around whoever I play.
If you can't play at 6, then pick a time Monday that you can commit to. If you can play at 6, then tell them that and be sure to be there.
You can set your phone up to get notifications on Slack too. In fact, you should set that up. But we need to know in here that the game is scheduled and what time so guys can tune in to watch. If the game doesn't get played, we can come back here and see that x player committed to x time and no showed and then they would be placed on auto.