Using the term waveform implies the behaviour of the signal over time, so reference to time is redundant. If you do want/need to be explicit about time, then I would suggest any of "temporal behaviour of the signals". I would choose "behaviour" since this is a digital interface, and I assume what is of interest is the timing of signal changes relative to one another, rather than say, their frequency, waveshape or amplitude. But without more context that could be completely wrong.
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