Do they like to be in the sun? Direct or filtered? Should they be watered weekly? Or only when soil is dry to touch?
Care of Oxalis Houseplant
Oxalis prefer morning sun and filtered light later in the day. The development of legginess is usually an indication that there's not quite enough light.
For water, that depends on your soil (well draining or moisture holding) and how dry the surrounding air is. Try watering every 3 to 4 days. If you see wilting, add water. Assuming this corrects the situation, you now have a good idea of the ideal timing for your situation.
Here's a guide with good information about planting and growing oxalis: https://www.leafari.com/oxalis-shamrock-planting-guide.html