Currently you are only able to back date a start date i.e. You can't set a future start date.
When you join a challenge, the challenge will automatically start on that date. If you want to start on a different date from the day you join you will need to backdate the start date.
To backdate the start date once you have joined the challenge:
- Log in to your My Virtual Mission account and go to the main page for the challenge
- Go to "Mission Control" at the top and select "Set timeframe"
- Here you can set a timeframe in weeks and backdate your start date
- Make sure you save the changes