Brave Elena, why would you pick such a challenging cook for your first effort?
Never mind that.
I suggest putting all the fish in your freezer until you come to an understanding of the fundamentals of the sous vide cooking technique. Why not start with something you enjoy, but is simple and forgiving?
Maybe chicken breasts or pork chops?
If you want to persist in your seafood adventure, why not select a temperature that’s where the two recipes’ temperatures overlap? That would be reasonable and somewhere in the middle won’t do much harm to either of the fish in those short recommended cooking times.
You don’t reveal the thickness of the fish you plan to cook. I hope they are similar just to make your life less complex.
May i suggest you consider your new Sous Vide Cooking Rule #1 to be that cooking times are based on the thickness of the food to be cooked?
I know, this is not what you have been doing.
That’s why it is your new rule.
What do the recipes inform you?
You may have noticed that there is a 50% difference in the longer cooking time to the shorter. That’s to allow for variations in the thickness of your fish.
Your next decision is cooking temperature. In general, and particularly for fish, the higher the temperature the firmer your cooked product will be. Some people like their salmon melt-in-the-mouth soft and tender while others prefer solid and flaking apart. It’s all up to your sensory expectations. You are in complete control with your new cooking technique.
The halibut is a large wild caught ocean fish that gets lots of exercise so it will be more solid than the salmon that’s considerably smaller and most likely raised in a pen or pond where it got little or no vigorous exercise. Those differences account for the different cooking times and temperatures you discovered.
To make your culinary life a little easier i recommend you maintain a cooking journal. Get a bound book and keep it in your kitchen. Record every cook by product, size ( usually thickness), temperature, and length of time. One last detail, - the outcome. Was is amazing?
If not, note what you might do next time to achieve a better result.
Feedback is the breakfast of champions, - particularly when it comes from yourself. By recording each cooking experience you will be tailoring your cooking techniques precisely to your tastes.
You are the only expert on Elena, so only rely on recipes as starting points.