For instance, how long should I cook a 25 oz steak at 65 C ?
Shuja, like most things in life, it all depends. You don’t provide enough detail to assist you.
In SV cooking weight is unimportant. For success with your Anova PC you need to adopt a new way of thinking in terms of the important factors of temperature, time, thickness, cut of meat and desired outcome. For example, I hope you wouldn’t cook a round steak the same way you cook a thick rib steak of the same weight. Right? Or not?
We all have different tastes and thresholds of acceptability regarding doneness. What’s yours?
Lots of good information available here: Sous Vide Steak Guide | The Food Lab
With sous vide, thickness (and the cut / type of meat) determines the time you’re going to cook it. Level of doneness desired determines the temperature.
Umm…at 65C, you know that’s a pretty well done steak, right? 
If you use the search function above, you’ll find there’s lots of links to thickness charts that you can bookmark for future use.
Hey @Shuja! Welcome to the community - I see you’re new here. Please note that with sous vide, it’s thickness that matter, not weight. How thick were your steaks? We’d be able to help you out with finding out the recommended cook times based on this. @fischersd also dropped a very useful link from Serious Eats. Tells you everything you need to know about cooking steaks! Certainly helps to get more information on this! 
-Alyssa
That’s actually in the medium-well range.
Yep…it is. I know…shouldn’t throw personal bias’ out there.
I had once bought from a butcher a 2" wagyu ribeye, about 650g, cooked at 52°C for about 80 minutes (20 extra minutes from what the default 60 min suggested by the anova app), and it turned out fine!
I have had the sous vide for over a year now and been using the Serious Eats steak cooking guide times with perfect results through out this time. However, for the first time I was cooking for 10 people so cooked 3x pieces totalling over 3 kg of Scotch Fillet and after 3 hours the meat was undercooked - a time and temp that has worked countless times for me in the past.
While Serious Eats talks about a steak being 2 inches thick they dont talk about times over this thickness. Are there any guides anywhere that provide this info?
Sasha, yes, there are many thickness and time SV cooking guides available in both print and on-line formats. You can also develop your own reliable SV guide based on your detailed SV cooking history.
We have to have your cooking details in order to help you discover the cause of your undercooked steaks. You are providing unhelpful details such as number of people and total weight.
For example, - what degree of doneness were you aiming for?
What water temperature?
Meat thickness?
The following site has the information you seek:
It really depends on what you like for mouth feel. Me, I like my steak more tenderized, hence why I cook mine longer (heh - it was also partly by accident - wanted to have steak at night, so had to start the cook before I went to work)
Whoops - I was about to post the link to Douglas Baldwin’s thickness chart - I see Chatnoir has beat me to it! :). His chart goes up to 65mm (2.55") for slab cut meat. (once you get thicker than that, you really are getting more cylinder-like, hence the next column)
Thanks Chatnoir for the link.
I checked the times and there is a lot more detail which provides the info I was after.
For your info I was after a meat temp of 57C (medium rare according the meathead guide), water temp the same, which I had cooked for 2.5 hours. Based on the tables you sent the link, for an 80cm (which was circa what my 3 cuts were) I should of cooked for something over 4 1/4 hours.
I look forward to using the info going forward.
All the best
Thanks Fischersd for your response.
All the best