You can't see botulism. It can and does grow in a vacuum and it will develop if given more than about 4 hours to grow at temperatures less than 121 degrees. Given that you don't have an actual circulator, the water temp in your rig is going to fluctuate. I would think twice about eating that if I were you.
The basic idea is that if you set your temp control to 120 degrees, and assuming it works and holds your water at that temperature, your food will reach but not exceed that temp at a certain point in time. Obviously the food can't be more hot than the liquid you're cooking it in. After that point there is literally no benefit to continued cooking, as the temperature will not change, proteins will not continue to break down, and your food will not tenderize. The only way to actually make your food more tender is to go beyond 160-170 degrees where the connective tissue collagen begins to break down into gelatin. This is the falling apart tender stage which is achieved by 'low and slow' cooking methods. Obviously you don't do this with seafood but if you want to give it a shot, go nuts.
Regardless, once your abalone hits 120 degrees (lets say its a huge one and it takes 6 hours), the other 30 are pointless from the point of view of developing flavour, and inherently extremely dangerous from the point of view of cultivating potentially paralyzing toxin.