devcommands can be used to set the time of day, it's tod and a value 0 to 1

tod 0 (or 1) would give you midnight, tod 0.5 would be noon, tod -1 resets timekeeping

I to hope they add settings when creating a world, it's like Night/day in a flash

No it isn't possible to slow down the day/night cycle on vanilla Valheim, there might be mods available to preform such tasks