With self fertile, it only means that the plant can use it's own pollen. But if the stigma is too long, too far away from the pollen, you'll have to depend on your insects to pollinate. So because of the time that the flower opens, typically at night, the insects are not as useful. In the morning, the pollen will absorb the moist night air and likely be not as useful for even insects to pollinate.
But if you have self POLLINATING varieties, that's better ... but general recommendation is that you hand pollinate regardless. Usually more pollen = bigger fruits.