For your viewing pleasure:

for entry in entries:
    if entry['time'] + 1800 < time():
        guild = self._bot.get_guild(int(entry['guild_id']))
        member = guild.get_member(int(entry['user_id']))
        if member is not None:
            if member.activity.name is not None:
                if member.activity.name.lower() == "league of legends":
                    await member.send("The 30 minutes has elapsed and you are still playing league, get banned.")
                    await member.ban(delete_message_days=0, reason='playing league')

You can read up on the conversation on the GitHub issue here.

TL;DR: the current system on the (unreleased) 1.0 codebase is that your Lemmy instance will replace all Lemmy URLs in posts/comments with the equivalent URLs on your own instance. In the issue I linked, some concerns are raised about this system and various other options are discussed. It’s possible that the way it works will change before Lemmy 1.0 is released.