Sounds like you are trying to develop or find a sophisticated side-channel attack against XOR encryption. Since XOR is my main type of encryption I also try to find brute-force and side-channel attack methods to test how secure or insecure my own XOR encryption algorithms are.
The XOR gate either passes an input bit to the output or flips the input bit in the output. Flipping a bit is probably a few clock cycles slower than passing a bit.
The first thing and experiment you would have to do is to check whether this assumption is really the case or not. In order to do so I would recommend to code your own XOR encryption function (in C++ or other language) and then add a timer which measures how long it took the program to execute or run through the XOR gate function in each of the two possible cases when input bit was either 0 or 1.
This way you could the test the clock cycle times per frame. As suggested by others the time difference may be so small that it has to be measured in nanoseconds precision. Most timer functions I know of in C++ and other languages, however, can only measure time down to milliseconds which is too slow for that kind of experiment, thus it seems impossible in my opinion to measure the time difference between each single XOR gate code execution. Unless someone can point me to a timer function (C++ prefered) which can measure systemtime in nanoseconds and output the time value into a variable.