Ask three people what khichdi looks like when it is ready. One may describe grains that still hold their shape, another a soft mixture that slips from a spoon. A third may want the browned layer at the base of the pot. Calling all three dishes by one name tells us something about the flexibility of Indian home cooking.
Rice and split mung are a familiar pairing, but the balance of grain and pulse, the water, the seasoning and the accompaniments all matter. Khichdi served with kadhi and pickle belongs to a different meal from a plain bowl made for someone who has asked for something familiar and soft.
When recording a household version, ask the cook how they tell it is done. That answer may be more valuable than a precise number of minutes. The comfort attached to a dish belongs in its story; promises that one version cleanses everyone who eats it do not.
Further reading: Ayurvedic medicine: evidence and safety (NCCIH)