What is the minimum separation for aircraft operating on or intersecting the same runway?
As both aircraft are still on a taxiway, turning into two different intersections it's absolutely normal. Each intersection has a so called "holding point" where all aircraft must hold until a clearance to enter the runway is given.

In this particular situation the tower controller will ensure that only one aircraft enters the runway and waits until departure separation minima are given before clearing the second aircraft for takeoff.

In this way maximum efficiency is reached by using different intersections as the following aircraft can line up (and hold on the runway; only after receiving a clearance to do so of course) immediately behind the first aircraft.