Is there an easy way to have my students sign up for time slots?

I teach an online course (undergrad). The final is going to consist of a phone discussion between myself and each student. They are going to take place on 1 day. Is there an easy way for each of them to sign up for a time slot?

I’d prefer not to get into an email back-n-forth. My thought it to break it down into two parts: 10–1, 2–5, during which they’ll call me. But where can they sign up? I’m going to have them call me (I think it’s better to have only 1 number being used than 18 for each student).

I thought about using Blackboard to start a discussion group, or giving them as assigned time each and if it doesn’t fit them, they’d have to email me, or having them email me their top two spots….and they’re online students so many of them work so…....there’s got to be an easier way!

Thanks for your thoughts and ideas…