I really like the idea of this solution; scanning the data pointer around the edge then moving to the inner edge! Seems like everyone else, myself included, did calculations to find the next element to copy instead of just moving it around. This is much easier to read, I would imagine.

I want to evaluate the efficiency of my solution.

This solution is best practice and clever it?

If you mean timeout limit, then it depends on language. For C, all kata time out after 12 seconds.

Timeouts for every language are specified in documentation.

How do I know how long my program needs to run?

unsigned char a=255;
char b;
b = (char)a;
printf( "a=%d,b=%d\n", a, b );