PartyTime

using System;
using System.Linq;
using System.Threading;

namespace ConsoleApplication1 {
    internal static class Program {
        private static DateTime _partyBegin;
        private static DateTime _partyEnd;
        private static DateTime _dt;

        private static int SetPartyWindow(int begin, int end) {
            _partyBegin = DateTime.Today.AddHours(begin);
            _partyEnd = DateTime.Today.AddHours(end);
            return end - begin;
        }

        private static string FormatWithTime(bool condition, string @true, string @false) =>
            $"{( condition ? @true : @false )} {_dt:HH:mm:ss}";

        public static void Main(string[] args) {
            int diff = SetPartyWindow(12, 20);
            string quitMsg;
            Console.CursorVisible = false;
            Console.WriteLine($"Set for a(n) {diff} hour party.");
            Console.WriteLine($"Party begins {_partyBegin:yyyy MMMM dd} at {_partyBegin:HH:mm:ss}");
            Console.WriteLine($"Party ends {_partyEnd:yyyy MMMM dd} at {_partyEnd:HH:mm:ss}");
            while (true) {
                _dt = DateTime.Now;
                bool partyTime = _dt.Hour >= _partyBegin.Hour && _dt.Hour <= _partyEnd.Hour;
                string msg = FormatWithTime(partyTime, "PARTY TIME!" , "There is no party at this time...");
                quitMsg =  FormatWithTime(partyTime, "Party's over :(" , "Goodbye");
                int buffDiff = Console.BufferWidth - 1 - msg.Length;
                Console.Write($"{msg}{string.Join("", Enumerable.Repeat(" ", buffDiff))}");

                if (Console.KeyAvailable) {
                    if (Console.ReadKey(true).Key == ConsoleKey.Escape) {
                        break;
                    }
                }

                Console.CursorLeft = 0;
                Thread.Sleep(1000);
            }

            Console.WriteLine();
            Console.WriteLine(quitMsg);
        }
    }
}