"After hours" means different things to different people. Just set up your DnD settings and let people message when and how they want, and then reply when and how you want.
While @channel is generally rude (unless it's something really urgent, and even then that's better solved by having one person specifically be interruptible for urgent questions), it's even better to just not check Slack after hours.
When is “after hours”? I check and respond during my work hours. It is likely to be “after hours” for some members of the team. I am sending this now so that they will see it when they come online. I do not expect them to respond 24/7 and will often mention that I’m looking for an answer “by tomorrow” to set expectations. And no, I don’t use @channel, though once in a while I will use @here if the priority is high.