Do it whenever you wake up. I guess the important part is that it should be the first urination of the day after sleep as that is the most concentrated
I know that at least the melatonin production in your body starts when the sun goes down and stops when your eyes are exposed to the sun once again in the morning. Unless you spend your early morning in the dark, the body's naturally scheduled melatonin dump should take place during your first urination, and you should do the practice then. I think capturing the concentrated first urination is the key to benefits of the practice and it shouldn't matter much if you sleep afterwards or not.
Thank you people for your comments. I have started my practice of amroli followed by sleep. It is said that the urine becomes Tamasik (negative) after the sunrise.so I wont break this rule.