After thorough testing of the other mods that promised to change the day/night cycle duration I was severely disappointed at seeing three recurrent issues.
So is this disappointment that has led me to develop my own day length changer mod. I specifically coded this mod to avoid the aforementioned issues, this below is how I have done it.
Also the mod is ressistant to the "/time set" command, as it recalibrates itself every time it is used. If somehow the cycle still breaks, by changing the cycle length for example (I honestly haven't found any other way to wreck it), both at sunrise and sunset the cycle is recalibrated and fixes itself.
Configuration is done through a single gamerule: dayLength
Write: /gamerule dayLength (Time in ticks)
The default vanilla daylight cycle length is 24000 ticks (20 min), so a 48000 ticks (40 min) cycle length is twice as long as a vanilla cycle. In case day length is set to a number equal or lower than 24000, the day will have the normal vanilla day length.
WARNING: If you are using shaders that sync the clouds to the daylight cycle they will also be stopped at the checkpoints, to avoid this find an option that desyncs them. With Complementary Shaders for example:
Install Euphoria Patches > Settings > Configure Euphoria > World > World Time Animation: True
WARNING: If you have tried another day-elongating mods before mine, they might have left your world's ticking system damaged upon uninstall. Sadly I haven't fount any fix to it other than creating a fresh world. In case you uninstall my mod, the only necessary step to take in case of the day-night cycle being frozen is setting the gamerule doDaylightCycle to True, that should permanently fix it to run the vanilla way normally.
Feel free to use this mod in any modpack you want and comment any issues you find, but I won't probably be checking too often, so please be patient.