No, the Sonos One SL has no Bluetooth connection for music. It does have a Bluetooth Low Energy system for setup, but that’s not enough to carry a music signal. 

If you wanted to add a Bluetooth connection, I’d recommend a Roam be added to your system. You could then send the Bluetooth signal to the Roam, which could then be “grouped” with the Sonos One SLs, and they would all play the bluetooth signal. 

Let me ask you this… 

Say I got the roam, would it be possible to play music through airplay and use a timer app to send sound via bluetooth?

Can you perhaps give details of the App you’re referring to and what your looking to achieve, as that may help to answer your question.

I use the system for my gym. We would like to have the timer be able to project sound to the speaker so trainers can manage the class. 

The short answer is no. You would need to physically be there to change the input from AirPlay 2 to Bluetooth, it wouldn’t be (I’m 90% sure) automatic. 

So say you wanted to play music for the class via AirPlay 2. That works fine. But the system would not automatically switch over if you sent a Bluetooth signal to it. That would require someone going to the room that was the Roam, and changing the input. All the other speakers, being “grouped” as a room, would still play that new input, that’s not the problem, it’s the initial room.