The heat and the cold get the attention. The thirty seconds between them do the work.
We call it the threshold — the pause at the line, after the sauna and before the plunge, or after the plunge and before you leave. It is where the body catches up to what you have asked of it. Skip it and the crossing is just two temperatures. Keep it and the crossing becomes one thing.
Stand at the line. Do not rush it. The reading settles in the gap.
A reading from Meridian.