Users can definitely post the same individual more than once in a day. The general guideline:
An observation records an encounter with an individual organism at a particular time and location.
refers to photos taken in quick succession where nothing has really changed in the meantime. As you say different stages of development that might occur on the same day are totally fine to separate into different observations. Egg and then juvenile; flowers open during sunrise and closed at noon; mushroom emerging in the morning and developed in the evening.
More discussion about this guideline can be found here:
https://forum.inaturalist.org/t/what-is-an-observation/3367
iNat is my nature journal. For example for plants, I find it interesting to see how individuals are developing/growing, or, in my urban locale, being managed over time. So I might observe the same individual weed in a sidewalk crack multiple times. : )