Is there any data on this anywhere?
Well I am an electronics engineer, mechanical engineer and physicist, and I developed scuba diving computers and timing devices and ultrasonic communication systems for many years. The two main sources of error in the stackmat will be:
1. Manufacturing deviation in the crystal oscillator used to keep time (error in ppm)
2. Unit-to-unit variance in the capacitance of the finger-touch sensors (this means that some stackmats will 'start' and 'stop' faster or slower than others when you touch your fingers and/or remove them)
Of these the second will be the greater source of error. The first would give an error of around 0.0001 seconds on a 5 second solve, depending on the quality of the crystals. The second source will be much greater and could be as high as 0.01 seconds and this error will be fixed and not related to the length of the solve. Without knowing the exact construction of the finger touch sensors and the various quality checks in their manufacturing process it is hard to say exactly how big the error is.
For the less technically inclined this means that if Felix had done the exact solve on a different stackmat the recorded time could have been as much as +/- 0.01 seconds higher or lower.
Mats did 4.744 +/- 0.01 = 4.734 to 4.754
Felix did 4.737 +/- 0.01 = 4.727 to 4.747