This achievement is earnt at the end of Deathloop, once you've completed all visionary leads and have Aleksis, Egor and Wenjie join the Updaam party. To make this easier on yourself,
enable Infinite Reprisal's, One Shot Kills and set Loop Stress to Minimal in the Gameplay Options menu.
My loadout was made up of "Tribunal" (Silenced) weapon, "Aether" slab with "Flicker" & "Erase" upgrades, "Shift" slab with "Airborne" & "Reach" upgrades.
Karl's Bay (Morning)Sabotage the Fireworks to kill Frank.
One shot Harriet in Hanger 2.
The Compound (Noon)At Egor's experiment, deploy a Nullifier and enter the code.
Fristad Rock (Afternoon)One shot both Charlie and Fia in Bunker 9.
Updaam (Evening)One shot Aleksis, Egor and Wenjie.
Exit the level via the Rakyetoplan (Rocket).
Either choice to join or kill Jullianna will make the "One Perfect Day" achievement pop.
See my video guide for a full walkthrough: