Recently got an immersion heater and vacuum packer and I’ve been experimenting with lots of sous-vide cooking. This ‘roast’ beef (gently cooked for 24 hours then finished on a hot griddle) was great, so smooth and rare with still a lovely browned crust.
For those roasts in your freezer, try 4-6 hours for tender cuts and 12-36 for tough ones depnding on size - you’ll get that bloody center you want with less time in the bath.