To install: Rename the downloaded .zip to data3.pak and place it into the DW folder located in your Dying Light Directory.
To install Out version: Place the Out folder into your Dying light folder located in Documents.

v1.1 change: Edited difficultyparams.src to remove the day and night multipliers. As higher difficulties would make nights last 2x as long, and also make days last shorter, and well, that's just silly and ruins the effect this mod should have. No Death Penalty also edits this file so a patch will have to be made by yourself.

Making this mod was fairly easy, taking a look at other mods that did this, to see which file they edited, I took a look at the original file, and there's one line that gave it away

export float WHOLE_DAY_DURATION__DAY      = 5760.0;// 1h in game daytime means 4 minutes of real time
export float WHOLE_DAY_DURATION__NIGHT    = 1260.0;// 1h in game daytime means 0.875 minute of real time
export float WHOLE_DAY_DURATION__INTERIOR = 8640.0;// 1h in game daytime means 6 minutes of real time

meaning 86400.0 would equal 60 minutes of real time.  

So I changed those lines to this

export float WHOLE_DAY_DURATION__DAY      = 86400.0;// 1h in game daytime means 4 minutes of real time
export float WHOLE_DAY_DURATION__NIGHT    = 86400.0;// 1h in game daytime means 0.875 minute of real time
export float WHOLE_DAY_DURATION__INTERIOR = 86400.0;// 1h in game daytime means 6 minutes of real time



Note: Scripted events like missions still advance time, so the transition will be pretty noticeable when it happens. Think of the Dark Knight Rises.