This mod is deprecated and does things in a suboptimal way, on all surfaces, which might interfere with other mods.
Please use Clockwork or other mods which don't have these issues and offer more features (like changing dawn/dusk times).
It's perfectly safe to remove this mod from the game and install any other one at any time.
Makes days and nights 4x longer (by default) and multiplies accumulator capacities by the same value.
Factor is adjustable via Mod Settings menu (Startup tab), changing accumulators can be disabled there too.
Kinda like Day Night Extender, but in 50 lines of lua instead of ~500, with proper Mod Settings affecting accumulator adjustments, and updated for 0.17.x.
Accumulator capacity adjustment is meant to have them last same time as before when using solar power (4x night length means they need to last longer), but note that it will apply to non-solar uses of them as well, hence the setting to disable this extension in the Mod Options (e.g. for those who never build solar panels).
Whole default day/night cycle is ~7 minutes at 1x game speed, see Factorio wiki Time page for nice visualization and more details. Also check out Time Tools mod for an in-game clock, easy game speed controls and circuit network elements to track time-of-day on a weird alien worlds.
4x adjustment will stretch full 7m cycle into 28m, prolonging all phases of it proportionally.
This mod does not have options to affect specific phases differently (yet?).