I confess I'm not familiar with the term entrecôte, but looking it up, its pretty clear this is a already-tender cut. So you don't need to tenderize it.
In fact, you probably don't want to tenderize it—at some point, it'll go from tender to mushy. Unfortunately, from frozen, at least according to the Baldwin tables, you'd need over five hours. If you additionally want it pasteurized, that'd probably be over six hours, but he doesn't have a table for that. Either of those times is risking mushy, at least on the outside.
You can reduce the heating time substantially by thawing it in the fridge. This also gives you the opportunity to sear before bagging (killing any surface bacteria, and also improving flavor). You're probably looking at around 3–3½ hours this way (maybe up to 4 for pasteurization, depending on exact thickness).
Finally, once its thawed, you could split it in half, giving you two, 25mm steaks (split before searing, of course). Then you're looking at around an hour in the water bath, or two for pasteurization.
Even with a pre-sear, you'll want to sear after cooking as normal, too.
Your final option is to up the water-bath temperature a bit, and pull before the steak reaches thermal equilibrium. Basically, the last few degrees take forever—heat transfer is proportional to the difference in temperatures—so if you're OK with a doneness-gradient, as you'd find in traditionally-cooked steaks though not as extreme, you can do this. Problem is, I don't have a table for this, so I'm not sure what the time would be at, say, 59°C. You could attempt to rig it with a probe thermometer to find out, but beware cheap probes are not waterproofed where the wire enters, and will be break if water gets there. There are i-Device apps that will calculate these times for you (PolySci Sous Vide Toolbox, Sous Vide Dash) but I haven't used either (no Android versions...) [This is called the deltaT method]