After the seeds have sprouted, should the initial stem and cotyledons be kept under direct sunlight or indirect sunlight, assuming watering once a day?
At what stage should they be moved to direct sunlight, if at all?
In a bright place, but not direct sun - no tiny seedling likes direct sun much. Direct sun should be fine once they've got going, been individually potted and got 10 sets of leaves as a minimum, but not if you're in the tropics and the midday sun is extremely hot.
I have two pots of citrus seedlings going right now (pomelo and key lime), and am finding that in my location near the US/Canadian border, they are very happy in a south-facing window with direct sunlight. As Bamboo mentioned, your latitude is going to be a consideration.