Morning. Though I should probably be doing both. But I tend to sleep in odd positions which can make me stiff when I wake up.
Yes i think stretching in the morning is better you start your day with a great power and your muscles also relaxed and you can also have a workout at the night so you have a certain routine that is so easy to do and not stress you
I find that stretching in the morning is easier, but I do believe stretching at night can be better because your body has been busy all day. So you need to stretch out those long walks, work schedules or even school days.
I try to stretch at both times of the day but I like to sleep in as much as possible and also like to stay up later so I find it easier at night to focus and stretch properly.