Universal Shorter nights, skip every other

Hello in short words,

i look fir rust plugin which makes nights not so dark , and skips each 2nd night instead of each night

and

plugin which executes command or plugin
on player count like when there is 20 ppl online command executes
and when is less than 20 it turns off plugin

thanks

 

ok , and do you know how to code something that makes plugin or command run when there is 20 ppl for example xmas or rgive plugin