Standard seems to be 1 second.
At least the serial monitor shows ~3 seconds:
no "WIFINAME" found, reconnect after 1s
I would like to extend this interval significantly, but could not find anything in the docs.
If this were possible I could use it as an alternative to my problem here
RECONNECT PROBLEMS WITH WIFI, SOMETIMES LOOSING RAM
ESP8266 with 3.0.2