Thanks for the replies!
Manda, I always feel more energetic in the afternoon so maybe that theory is right! I definitely enjoy it more and am more likely to do it in the afternoon, so I'm going to stick to that.
Patientperson, I feel exactly the same - if I don't have breakfast I feel all wobbly kneed and if I do, I feel sick. Can't win!
Thanks again for the help guys, it's nice knowing that it's not just me that's not a morning person