It is always a good idea to mix things up
I used to do yoga at 7am and if I hadn't eaten in the evening I couldn't do the session as I got really dizzy - lack of energy and low sugar levels.
I had to alter my routine to different times on those occassions. I must say that I also enjoy doing yoga early evening as I am warmed up and the stretches are deeper than firsth thing. I use the mornings mostly for long deep stretches and waking up - ie tadasan and spinal warm up and tend to do a more integrated longer session later. It's finding what works.
Muscles are weaker first thing due to being inactive and laying down so it can take a while for them to warm up.