The Upload Deadline is the grace period following a challenge end date that allows all members a fair chance at uploading their activity prior to the results of the challenge being determined and announced. The Upload Deadline will always be in the your own timezone.
For personal challenges, the upload deadline will always be 24 hours after the challenge end date.
For company challenges, the upload deadline can be anywhere from 24 hours to 7 days following the challenge end date.
Make sure to check out the "Challenge Rules" for your challenge to learn when the Upload Deadline will be.