The Twitter bot process had some issues the last couple days. I restarted it, so it should be functioning as normal now.
The Twitter bots check their status about once per 30 minutes, so the bot should respond in that time frame. Note that Twitter will reject tweets that it thinks are duplicates. So if you bot is always using the same response, Twitter may be rejecting them. You should see these errors in your bot's error log though. Is this with your bot SHOCC? I did not see any errors in its logs.
You should also see your bot's response to mentions in its chat logs, under the Chat Logs page. If you see the response in the chat logs, but not on Twitter, then Twitter most likely rejected the response.