I have the same problem. I bought SONOFF 4CH PRO (not R2) and I have the same delay as a SONOFF 4CH PRO R2. The minimum value is 1s. (The configuration used is s6 = 1, k5 = 0 and k6 = 1111).
Could anyone help me please?
Do you know if all the 4 SONOFF that works at 250ms have the same version of firmware than the SONOFF that works bad?