I was first exposed to the idea of cold showers for better health in Veritasium's "How to Slow Aging (and even reverse it)" https://www.youtube.com/watch?v=QRt7LjqJ45k. The video isn't focused on cold showers exclusively, but he briefly touches upon it as a method of improving longevity. I figured that implementing cold showers into my daily routine should be a pretty easy task, because it doesn't add any extra work into my schedule--it's just replacing a small portion of my hot showers, which I should be minimizing anyway.
And yeah, you're probably right about cold showers being less of a good idea in the evening. How often do you shower then? I can't bring myself to go to bed at night without feeling clean, but showering twice in a day also feels a bit time-consuming and excessive.