This is a wonderful and useful phrase I highly recommend to all students of Czech. It’s meaning is quite simple. It’s an expression of frustration at wasting time. For example, as you sit in the restaurant after the meal endlessly waiting for any member of the staff to approach so you can pay the bill, you can say that it is „jak když sere a maluje“. In fact, this is perhaps the most expressive way of declaring such dismay in any language, because it’s literal translation is „like when one shits and paints“. As an artist, and a daily shitter, I can relate.