Yes, that is true. If your longest days are only 10-14 hours long, you need to grow short day onions. They are the only kind that can get their bulbs to mature with less daylight. Downside, they tend not to be great keepers.
People who have 16 hours or more of daylight can grow the long day onions.
In mild climates onions are planted usually from seeds not sets in the fall. The tops grow through the cool months and the bulbs will begin to mature as the weather warms and the days get longer. It takes about 5 months from seed to harvest.
I planted my awahia and Texas granex in October last year and they started bulbing up in March and they are ready now. I can usually plant seeds between October and November.
I can't start from sets in the spring since they won't have enough time to mature and the sets that are sent here usually are not the right kind.
Happy gardening in Hawaii. Gardens are where people grow.