The actual time it takes one instance of eValid -- a "browser user" or BU -- to load and start playing back varies with the power of the machine it is running on.
Even on smallish machines this time is less than 0.5 seconds. In some runs we've made for customers that involve use of very high-power machiens "in the cloud" that time is reduced to about 0.1 seconds.
As they say, "...your mileage will vary..."
A related question that comes up often in relation to browser launch speed is, "how do I get 1,000 browsers to all start playback at the same time?" For that we recommend putting a "synchronize on text" command at the start of each playback, where the text is supplied by a web page that YOU control. Change the text to that the synchronization will succeed, and that browser will start up. We've done this with 1,000 BUs and the resulting impulse of load on the server under test brought it down. Simultaneity is the key on this.