Andrew, yes, it's frequently addressed here but i can't seem to find my previous detailed comments here either.
To answer your questions:
- You can always cook from frozen.
- Always use your usual cooking target temperature for sirloin steak unless you want a different doneness result. No temperature change, no result change, every time. Isn't your Anova wonderful?
- No. Do as you always do, start by preheating your water bath to the target temperature.
- I do not understand how water can adjust itself.
Consider what happens.
Your Anova applies heat to water up to target temperature, you add frozen steaks, water temperature drops, Anova keeps on heating and water returns to target temperature, steaks cook as desired. Andrew is happy as long as he doesn't go changing the temperature sometime in the process.
What about the time?
You have some options.
You can guess, add an hour, use a larger water vessel, or precisely cook your steaks to your desired degree of doneness based on your SV cooking knowledge and the undisclosed thickness of your frozen sirloin steaks.
For 1-inch thick steaks the cooking time will be about 1 3/4 hours at your target temperature based on your desired degree of doneness which is alright to keep a secret as it doesn't really matter to anyone else.
For 1 1/2-inch thick frozen steaks, about 3 1/4 hours will do you.
If Andrew is a big spender and has 2-inch thick frozen steaks they will need 5 1/4 hours to be cooked as desired.
If you are interested in adding to your SV knowledge bank you might find it useful to refer to the following resource: