There won’t be delay for audio input. Technically there is, but at the start of streaming and it should not be detectable since there’s nothing to reference it to, so all speakers will be in sync. 

You could set up the Era in a different room, with the turntable connected to it, and just have it play to your current One SL’s. And even have the Era playing a different source in that room, even whilst playing the turntable audio to your One’s. 

The delay ​@nik9669a is referencing is when the audio enters the Sonos ecosystem. You won’t hear any delay on any Sonos speakers, they’ll all play in sync. If you connected other, non-Sonos speakers to the turntable in some way, not going through a Sonos device, you would be aware of that delay. 

Thank you