no, i don't think so, as long as it isn't too unreasonable.
i often put "late times if possible please as i live a long way away" (because i have to feed all the others before i can leave) and they can either ignore it or be helpful... usually the latter.
I have, often like kerrilli put late times as a 3or4 hour journey and havent eveer been balloted as yet-but then i didnt do much BE last year so i used a ballot sticker on each one
I often ask for times if possible to be either early or late on (depending on when my class is during the day and how far we have to travel etc.). They have almost always managed to do so.
I have often asked for early/late times or day before dressage and they either do this or ignore it!!! Never got balloted last year. At local events I often volunteer for early times, so don't feel so bad asking for late ones when travelling further!!!