SFComment.user.js

// ==UserScript==
// @name         SFComment
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Some SF comment window hacks
// @author       roylez
// @include      https://canonical*.visual.force.com/servlet/servlet.Integration*
// @license      MIT
// @require      https://code.jquery.com/jquery-2.2.4.min.js
// @updateURL    https://gist.github.com/8633e9b59406030f9c297b3e54e97e7b/raw/SFComment.user.js
// @downloadURL  https://gist.github.com/8633e9b59406030f9c297b3e54e97e7b/raw/SFComment.user.js
// @run-at       document-idle
// ==/UserScript==

function inject_css() {
    $("head").append('<meta name="viewport" content="width=device-width, initial-scale=1">')
    $("head").append('<link ' + 'href="//unpkg.com/tachyons@4/css/tachyons.min.css" ' + 'rel="stylesheet" type="text/css">')
}

function update_timecard(window) {
    var w;
    if (typeof unsafeWindow != undefined) {
        w = unsafeWindow
    } else {
        w = window;
    }
    var timecard = $('input[name="vfpage:caseForm:caseBlock:CommentsSection:TimeSpentRequired:timeSpent"]')
    function listener(event){
        if ( event.data.timecard && !timecard.val() ) { timecard.val( event.data.timecard ) }
    }
    w.addEventListener("message", listener,false)
    timecard.on("focusin", function() { w.parent.postMessage("getTime","*") })
}

function default_inputs() {
    let status = $('select[name="vfpage:caseForm:caseBlock:CommentsSection:StatusRequired:caseStatus"]')
    status.val("Waiting on Customer")
    let comment = $('textarea[name="vfpage:caseForm:caseBlock:CommentsSection:CaseCommentRequired:caseComment"]')
    comment.addClass('code black bg-washed-green db border-box hover-black br2 b--black-20 w-90')
    comment.val("Hello,\n\n")
}

inject_css()
update_timecard(window)
default_inputs()