How long does it take to flash a WRX ECU with ATLAS?

There is no single number, because adapter speed is the dominant variable and the supported adapters differ substantially. Reading and flashing an ECU is a bulk data transfer. A faster interface moves that data more quickly, and ATLAS's supported adapters span a wide range. The OBDX Pro VX is described as lightning-fast. The Tactrix OpenPort 2.0 is the traditional benchmark. The OBDLink EX is explicitly noted as slower than the OpenPort. Various ELM327 adapters connect over serial and vary enormously in quality and speed. So rather than planning around a specific duration, plan around the practical requirement. ATLAS guidance is that the vehicle should have ample battery capacity to supply the electrical system for at least 30 minutes with headlights and auxiliary components turned off, and ideally be connected to a high-amperage battery charger. That 30 minute figure is a useful planning horizon - it tells you what the setup needs to tolerate. The practical advice that follows: **Give yourself an unhurried window.** Flash in your garage or driveway where the car being unavailable for a while is an inconvenience rather than a problem. Never in a car park before you need to drive home. **Connect a charger.** This removes duration from your list of worries entirely. Without one, a slower adapter genuinely increases risk because it extends the period the battery is carrying the load alone. **Do not interrupt to check progress.** Touching the adapter, the ignition or the laptop mid-flash is one of the two leading causes of a failed flash. Let it finish. **Buy the faster adapter if you flash often.** If you switch between a pump gas map and an ethanol map regularly, adapter speed stops being a one-time consideration and becomes something you experience every time. If a flash seems to be taking dramatically longer than your previous ones with the same adapter, that is worth noting afterward - but do not intervene while it is running.