Super looking tri-tip.
As you are probably aware, there's no harm in going longer in a sous vide cook; but, I'm not sure that you're going to see much difference in texture with the extra 2 hours, as there's not a lot of collagen and fat to break down in a tri-tip. If you think that it's a bit on the tough side, consider using a quick marinade with papaya to help break down the proteins a bit more. Be careful, if you marinade it too long (or put it inside your sous vide pouch), it might break down too much and get mushy. I'd start with 30 minutes to an hour. Almost forgot, don't put it in the fridge, the papain reaction doesn't happen at low temps.
Here's some info from one of my favorite sources - AmazingRibs.com
Fresh pineapple, papaya, and ginger have enzymes that tenderize meat. Papain, the enzyme in papaya, is an enzyme in papaya and the main tenderizing ingredient in Adolph’s Meat Tenderizer. These enzymes work fast. Within 30 to 60 minutes the meat is ready for the grill. Alas, pineapple and papaya add very little flavor to the meat in such a short time. Some people like the softer meat, others feel it is mushy. You decide. The enzymes are destroyed by the canning and bottling process, so be sure to use fresh pineapple, papaya, and ginger if you want the tenderizing.
A bit more info: http://www.indiacurry.com/faqhints/papayatenderizemeathow.htm
Also, pineapple and kiwi fruits also contain enzymes that tenderize meats. Again, be wary of too long contact or risk the mushy meat syndrome!