I have seen numerous news sources claim that for over half an hour LEOs were on site of the shooting but doing nothing.
Department of Public Safety Director Steve McCraw told reporters that 40 minutes to an hour elapsed from when Ramos opened fire on the school security officer to when the tactical team shot him
Juan Carranza, 24, who saw the scene from outside his house, across the street from Robb Elementary School in the close-knit town of Uvalde. Carranza said the officers did not go in.
From CBS, emphasis mine:
A specialized tactical unit made of local, state and federal law enforcement officers were eventually able to enter
Is it true that LEOs were on site, but were not doing/not able to do anything to help?