Not optimal but you may need to measure the real thing or move on.

Unsure of the Toto but if this is a retrofit you also want to check the supply location and compare to manufacturer's instructions or an actual product example. While I primarily install new and we move a lot of stuff, my recent retrofit to accomodate a Kohler Flora involved moving the supply & drilling the floor anchors thru porcelain tile (hard material).

There remains almost 2" behind the toilet with an original 12" rough in to the studs.

Most of the Toto washlets have specs with the electrical outlet on the left side, close to the water supply.

This is going to be frustrating but the Toto shows the water supply approx 11.75" left of center. I know becuase I had to move mine and I'm reviewing the install diagram. That is likely a "safe" number and others may work but you'll need to see the unit in person. (AI has a different answer BTW)