Set round dates on a Challenge Ladder
A Challenge Ladder round is a stretch of days, so a round needs two things: when it opens, and when it closes. You set the opening date per round and the closing date follows from the round's length.
On the Matches tab, open the admin menu and choose Manage Round Dates.
How many rounds the season has
There is no separate field for it. The rounds listed in this dialog are the season — add a round to extend it, remove one to shorten it.
A round that already has scores in it cannot be removed. Clear or void its results first if you really need it gone.
Start dates
Tap a round to pick its start date. That is the first day the round can be played, and it is what decides whether the round is open, still to come, or finished.
Give every round a date before you pair round 1. Pairing reads these dates to work out each match's play-by date, and a round with no date has no window to play in.
Plays until
Under each start date is a Plays until line showing the last day of that round. By default it is the start date plus Days to play each round from the ladder's settings.
Tap it to give that round a different end date. Use this when the calendar gets in the way — a round over the holidays that needs an extra fortnight, or a short round to line the season up with a finals date.
Two things worth knowing:
What is stored is the round's length, not the end date itself. Move the start date later and the round keeps its length, carrying its end date with it.
Once a round has its own length, an undo control appears next to it. Use it to hand that round back to the season default.
Overlapping rounds
Nothing stops one round's window overlapping the next, and there are seasons where that is what you want. Be aware of what it means: an entrant can have live matches in two rounds at once, and each still counts against that round's own challenge allowance.
Changing dates after a round is paired
You can. Match cards pick up the new play-by date, and a round you push into the future closes for challenges again until it reopens.
Tell the players when you do it. The play-by date is the thing they are organising around, and it moving without warning is how matches get missed.