easy going, both works...
you cannot upload without permission, so there is no way of making any mistakes.
if you buy the second voucher, you'll also settle an interview /
test appointment for you application. as soon as you get this date confirmed, you'll be able to upload.
as far as i know you can upload as close to that date as you want. i uploaded in the middle of the night, just a few hours before...
good luck!
jan