Short answer: Zalora is generally the fastest dedicated fashion app in Singapore because it offers express / same‑day options for in‑stock fashion items; major marketplaces (Shopee, Lazada) can match or beat that when sellers use express fulfilment. For true on‑demand (1–3 hour) delivery you’ll usually combine a retailer with an islandwide courier app (uParcel, GOGOVAN / GrabExpress) to get clothes delivered fastest. (Zalora.sg)

Quick details and how to get the fastest delivery:

• Zalora (fashion‑focused): shows express / faster delivery options and has dedicated fulfilment that often supports same‑day / next‑day for in‑stock items — easiest single app if you need clothes quickly. (Zalora.sg)
• Shopee / Lazada (marketplaces): many sellers offer express shipping or platform express fulfilment; speed varies by seller/warehouse but you can often get 1–2 day delivery or same‑day in limited cases. Check the “Fast delivery / Same day” tags in the app. (ParcelsApp.com)
• On‑demand couriers: if you need something in 1–3 hours, buy from a local store (or a fast‑fulfilment listing) and use an on‑demand delivery app (uParcel, GrabExpress, GOGOVAN) to rush it. These services advertise 1–3 hour islandwide delivery. (t.me)

Practical tips:

• Filter the app for “Same‑day” or “Express” and check the seller’s warehouse location / estimated delivery window at checkout.
• If you need it within hours, buy from a store that lists “same‑day” and arrange a rush courier (some retailers offer an integrated express option).
• Delivery speed depends on stock availability, time of order, and your delivery postcode — the same app may be fastest for one address but not another.

If you’d like, tell me your delivery postcode or a specific item and I’ll check current same‑day/express options and estimated times from the apps right now.