JSFiddle - React, Tailwind, and code Playground

JavaScript

var days = [5, 15, 25];
var hours = [6, 8, 7];
var result = [];

var a = 4;
var b = 22;

_.each( days, function( day, i ){
    if( days[i] < a && b < days[i+1] ){ // days[i] is also day
        result.push( hours[i] );
    } else if( days[i] > a && days[i] < b ){
        result.push( hours[i] );
        if( i > 0 ){
            result.push( hours[i-1] );
        }
    }
})

document.write( '[ ' + result.join( ', ' ) + ' ]' );