You can challenge teams 50% of your rank above you plus 2 positions.

If you win a defending match you are protected for 24h (no one will be able to challenge you).
If you win a challenging match you are protected for 6h (no one will be able to challenge you).
If you lose a defending match you are vulnerable for 6h (you will be unable to challenge).
If you lose a challenging match you are vulnerable for 24h (you will be unable to challenge).
You cannot play the same team twice in a row.
Time given to accept a match: 2 days
Team members required to challenge: 1
Players are allowed to be in 1 team at a time

This is a FAST ladder, protected/vulnerable times are halved normal ladders.