Groups operating on the free, BASIC plan can only run on the current month's board. ('Daily' and 'Weekly' leaderboards can also be viewed at any time highlighting the 'Monthly' button. See here for all the ways to view your activity.)
PRO Groups can create challenges of any duration and with any future start date via their PRO Admin Challenges dashboard. This means you should create your challenge on or before your desired start date - even if still operating on your free trial week. Count.It as policy does not backdate challenges.
If there is an active PRO challenge, that challenge will become the default view/leaderboard on the group homepage. Once the challenge has officially ended, the system will return to the default 'Monthly' board.
Users can always navigate through any past, present, or future challenges by selecting the "Challenges" metric and clicking on the left and right arrows on either side of the date ranges.
Check out the Count.It PRO plans and decide which one is best for your group!