How long to sous vide shoulder lamb chop?
Time will determine texture and your target texture is really up to you. Folks typically recommend the “pinch test”. Squeeze the bag and feel it out as you go. Once it’s pasteurized (id refer you to Baldwin for that data) you can shock it and throw it in the fridge and hold until whenever you are serving, so it’s best to start early. 

I haven’t personally processed this particular cut SV, so I don’t have a personal recommendation for you. I recommend keeping a log of every cook you perform with notes about texture so you can refer back to it in subsequent cooks. 

My gut tells me that anything in that listed range will work for you. They will just provide different textures. If you’re looking for tender, go longer.