Well there is much more to cold showers than just this. They energize you and yes they release a few really useful hormones to get through the day (plus boost testosterone in men for muscle building or whatever else ;) ). But I personally can not take a really cold shower before sleep as it energizes me too much and makes me restless. Hot showers on the other hand are the best before sleep so in conclusion start your day with a cold & quick shower and finish it with a nice & warm one :)