Short answer: For the broadest, fastest fashion delivery across Australian metro areas, THE ICONIC’s app is currently the fastest overall — it offers express next‑day and growing same‑day (including a “Twilight” same/next‑day option in Melbourne and Brisbane) and has cut standard metro delivery to 1–2 days. (mi-3.com.au)

Notes and alternatives:

• Many direct fashion brands (e.g., Sir the Label, Bond‑Eye, Sea Level and others) offer true same‑day or next‑day delivery to eligible metro postcodes via their own apps/sites — if you live in Sydney, Melbourne or Brisbane, check the brand’s checkout for same‑day options. (mamamia.com.au)
• Local same‑day courier/integrator services (Uber Direct/DoorDash partnerships, same‑day courier platforms used by boutiques) can make small retailers deliver within hours — so a boutique app using those partners may beat a large retailer for single‑postcode speed. (theaustralian.com.au)

Bottom line: If you want the fastest, most reliable nationwide-fashion app in Australia today, start with THE ICONIC’s app; if you need something in a single city right now, check the brand’s own app or whether the retailer offers same‑day via a courier/food‑delivery partner at checkout. (mi-3.com.au)