If you have OSA, you want it diagnosed. Getting enough good quality sleep will be critical to keeping your metabolism high through rapid weight loss. Folks who don't get enough restful sleep struggle more to get weight off and keep it off.
Also, if you have untreated OSA, the surgery itself is far more dangerous. The anesthesiologist will adjust the breathing apparatus, the anesthesia and your pain medication based on your OSA results. If you have it and it's not diagnosed you will more likely to have breathing problems in surgery or in recovery, and it will keep you from healing quickly after surgery.
So if you are diagnosed and it delays your surgery for a couple of weeks, consider those couple of weeks as an investment into making sure your surgery safer and your journey more successful. It is worth the wait to get this piece in line.