There are multiple deals starting at Dymocks' online store now, and in stores tomorrow according to their Promotions page. I've bolded the expiration dates as they're all a bit different.
20% off full-priced items from 25 December 2019 until 26 December 2019 at www.dymocks.com.au. Discount will automatically apply at the checkout. Discount is off recommended retail price and excludes special orders, books on hold, school texts, DVDs and CDs, Gift Cards and items already reduced.20% off all full-priced items for Booklover Members until 31st of December 2019 according to their recent post on Facebook.
50% off selected titles: Receive 50% off selected titles from 25th December 2019 until 31 December 2019 at www.dymocks.com.au. Discount will automatically apply at the checkout. See online for full list of titles.
Buy one book and get the second 50% off on marked selected titles. Discount is off the lowest priced book. Strictly while stocks last. See in store or online for full list of titles. Offer ends 27 January 2020.
20% off the publisher’s recommended retail price on all Lonely Planet titles while stocks last. See in store or online for full list of titles. Offer ends 27 January 2020.
Unfortunately there doesn't appear to be a free postage coupon like Black Friday :(
Wonder if that planet feels lonely too :)