Grinding for Balarak's Sash brush guide | Runescape 3 

also, it costs more, but it can be worth it to put a spirit attraction flask in a potion reservoir if you don't want to worry about paying attention to the timer.

You don't need to complete 'A New Age' to get the sash brush pieces . I've gotten all three pieces (the last two back to back). First piece at like 9ish hours , second piece at like 43ish hours, last piece at around 43.5ish hours. As long as you have the downstairs area unlocked in Daemonheim (and maybe you need to click on the book in the corner area,) you can get the sash brush pieces.