Yes, train them to 10 percent. After the new season starts they will be back to 80 ( or 99 percent but most probably 80 percent ) percent condition.

CUP games are played on the first day of the season. Timing will be known only after the new season starts.

Pro tip : Sometimes bugs creep in after the new season starts so be ready to take advantage of it.

2 season ago we had unlimited condition bug for 4, 5 hours 😂. Everyone who knew about the bug trained their players to godly level.