I just tweeted then on Thursday, so I went back to review my log. I sent my first DM at 4:43 pm CT and received a response at 5:20. So a 37-minute response time. Two subsequent responses took 11 and 18 minutes. I was in no hurry, so I didn't mind, though I did think it was a bit slow compared to the general Concierge phone line (MHC was off on Thursday, so I thought I'd try the Twitter route for the first time).