I woudl do it the week before O to make sure the meds have had a chance to leave your body.
Second q - I personally do not believe that salt sways a very large amount and in fact large amounts of sodium may affect fertility negatively which you want for TTC pink. I think the rapid weight loss and anesthetic outweigh any risk of the salt.
Plus, you will have the peace of mind from knowing that you get a clean bill of health prior to your pregnancy (PRICELESS!!)