21 September

At 12:12am on 21 September 2360, from atop a 400-foot-tall tree on Calderon Beta, one could see more stars in the sky than at any other point in history. According to the Eleventh Doctor, it was "like daylight, only magic". The Doctor took River Song there on their first date following her imprisonment in Stormcage. (HOMEVID: First Night, PROSE: Time Traveller's Diary)
Later in her personal timeline, River was chased across the galaxy by Sontarans to this point in time and space, and entered the Doctor's TARDIS. She called the Doctor a "nostalgic idiot" for returning to Calderon Beta, not realising that it was actually the same night and he was bringing her younger self there for her first time. An older Eleventh Doctor also brought a third River there on their last date from her perspective, before going to Darillium. She too entered the TARDIS, but was soon escorted out by her Doctor. The Doctor finally returned the second River back to Stormcage by vortex manipulator, and showed the first what they'd come for. (HOMEVID: Last Night)