> 3I/ATLAS was discovered on 1 July 2025 ... Initial observations of 3I/ATLAS were unclear on whether 3I/ATLAS is an asteroid or a comet ... observations on 2 July 2025 by the Deep Random Survey (X09) at Chile, Lowell Discovery Telescope (G37) at Arizona, and Canada–France–Hawaii Telescope (T14) at Mauna Kea showed a marginal coma with a potential tail-like elongation 3 arcseconds in angular length, which indicated the object is a comet.

https://en.wikipedia.org/wiki/3I/ATLAS

So, a day or so after its official discovery, maybe a week after its "pre-discovery"