Are some poses more appropriate in the morning and are others better in the afternoon?
Aside from the general distinction between such heating/energizing poses as Sun Salutes and backbends, which tend to be more beneficial in the morning, and such cooling poses as forward bends and certain inversions, which are more likely to calm one down in the evening, it really depends on the person.
If, for example, you are naturally a more flexible or "bendy" person, there is a case to made for practicing in the morning when you are a little bit tighter, and therefore less likely to injure yourself by overstretching. If you are naturally on the stiffer end of the spectrum, you may feel more limber if you practice in the latter part of the day, after you have been moving around for a while. Different factors come into play for everyone, so try observing the effects of your practice and of specific postures at different times of the day. Then make your determination, based on the way you feel both physically and energetically.