It all depends on the resolution of the imagery that you are using, more particularly the size of your area of interest (AOI) compared to the pixel size.
Let’s take the example of Sentinel-2 (which is commonly used to calculate NDVI) and your example area of 0.03 km2: your AOI would contain approximately 300 pixels which should be largely sufficient to monitor NDVI within the AOI. If you were to do the same with Sentinel-3 OLCI for example, then your AOI would be completely contained within 1 pixel (assuming a square shape for simplicity), but that pixel would return a mixed signal from your AOI and part of its surroundings. In that case, hard to get any significant information about your AOI…
I hope I understood your question correctly