I think you misunderstand timing sidechannels.
The idea is that (for example) if you compare two strings with length 15 you compare all 15 chars regardless if you find that the 3th char is already different.
You only need to be consistent with yourself. Stepping is completely irrelevant here.
An instruction that is constant time in one CPU may vary its time based on input in the next version of the CPU. That could still provide a timing channel in your example of a comparison if the comparison instruction finishes faster if, say, the left most bit is a mismatch.
I don't :) Basically you want all the code branches to result in similar (same) timings. Basic on the CPU and the data inputs those timing would vary, hence assembly alone won't do.
