when do you choose veil/tiara/accessories??

sooo at what point after you choose your dress do you do this??

i would think you can do it at any point but do many brides do this at the time they purchase their dress??

the problem is that i HAVE to order my dress this weekend because i will get $500 off.
ALSO the store will only have the sample in this weekend because it gets sent back to the designer for trunk shows after this weekend..
so technically should i be making these decisions now since i wont be able to try the dress on again until my dress actually comes in??
or is it normal to make these decisions around your first fitting (other than shoes of course) so that you can see the whole ensemble together??