Though it was initially one of those "sometime in the afternoon" appointments, I was able to call and get a closer estimate of their arrival around noon that day.
The plumber who showed up was incredibly professional, personable, and excellent at his job. He cleared the clogged line, and then also looked at the drains and aerators in every sink.
After he was done, all the plumbing in my house was in top shape. Fantastic service. It comes with a fairly high cost, but considering this is the first plumber I have ever had to hire, I felt it was worth the cash.