Those were launched on the same day.
The bands I like have concerts in different music clubs on the same day and I'm really not sure which one I should go to.
On the same day of my father’s death, Apollo 11 succeeded in landing on the moon’s surface.
You have the same day, which comes out to same day.
The readings follow the regular jukugo rules (on'yomi reading) but take note that 日 is read as じつ, the alternate on'yomi reading. You've been seeing this reading a lot lately, so hopefully you know it by now and it's easy!