The fantastic Sacred Heart Stores are open 7 days a week and quite a few Vinnies stores are now offering Sunday hours. You can also rely on Savers, which are open 7 days with some late night hours too. Although, not an op shop, I rate them as a store that promotes recycling.
Not quite your traditional op shop but the Brotherhood have an online second-hand bookshop called Brotherhood Books and it's fantastic! I ordered book at 10:30 Sunday night and they were at my place before 5pm Monday.
Hi Vicky, New recycled shop for Women Only opened only a few months ago in the Queen Victoria Hospital facing the Queen Victoria Square. It has designer, vintage and recycled clothes, some new. It is open Tuesday to Saturday 12-5 and all proceeds go to Fitted for Work. A not for profit organisation that assists women find work - for disadvantaged, long term unemployed. A brilliant organisation and the clothes are amazing. A hidden gem with amazing clothes and fantastic prices. Word is getting around slowly.
(I work there as a volunteer, as as the majority of the staff)