Most meditators say the best time to meditate is in the morning after waking; body is rested and the mind has not taken up the concerns of the day. Some will shower first, others just wash the face or dry rub it with a towel. Even though you have just been sleeping, lie down briefly and attend to relaxing the body and calming the breath. If you have to do asanas to get into your sitting posture, my bet is your chosen posture is not a good one.
Sitting later in the day should be preceded by a longer, more complete relaxation to reset the body and shed mental distractions. Systematic relaxation or 61 Points are options, and Yoga Nidra is possible if you are skilled with it.
The best time to meditate is in the middle of the night. A yogic saying is that yogis do their work while everyone else is sleeping. The classic brahmamahurta is from 3 a.m. to 6 a.m. Mind and body are rested, the world is asleep and there is less sense of having a limited period of time to meditate. If it is going well, you can stay, stay, stay…this is what you have been waiting for.
If you have found yourself not sleeping in the middle of the night, good news! For thousands of years, it has been natural to have “first sleep and second sleep” with a period of waking in the middle. Mind is awake but body is not inclined to move. The usual problem is getting out of bed. Don’t rush it but get yourself up, towel rub or wash the face, lie down briefly, then take your seat. Sit for an hour or more, go to bed for very restful sleep, and sit again if you wish. It’s the easiest way to quality sitting.