As many people stated before, Yoga is best in the morning, preferably outdoors for the fresh air. Afternoon does not give your body the same opportunities and you are simply more tired - less positive about doing any additional exercises including the topic one - Yoga.
Morning is probably the best time. Thats when people recommend to do it, but I guess it all depends on you;
apart from morning no time is suitable for the yoga , if its done in other time its not beneficial for your health , so keep its time in the early morning......
According to ancient myth and if we see the history then we will see that at all the places it is sugess that yoga sholud be do in the morning time , because in morning time our abdomen is empty and in that situation it is much better for our health.