According to my knowledge, the best time for exploring Taihang Mountains (天门山) in China, where you can expect drifting or floating experiences, is during spring and summer when the rainwater flows down from the hillsides.
In particular, 7 July might be a good day for this experience, as during the rainy season around late June to early August, you may encounter cloud-irrigated scenes on Taihang Mountains. However, please note that drifting or floating experiences are largely dependent upon weather conditions and water flow rates at the time.
Before planning your trip, I recommend checking local weather forecasts and water levels for better understanding of what to expect during your visit.