More specifically from SETS guideline...
" In auctions all order sizes and order types (market and limit orders) are tradable, ensuring a concentration of liquidity in the order book. All auctions could operate in the same way, whether scheduled or initiated by extensions or volatility events. The market participants are informed when the securities will be called for the auction. Each auction consists of two phases:
1. Call Phase:
Each auction begins with a call phase. The market participants are able to enter orders as well as modify and delete their existing orders. Each participant firm may enter as many orders to the order book as it wishes.
Information on the current order situation is provided continually during the call phase with members being able to view best bids and offers as they would normally during continuous trading, as well as being able to see an indicative matching price and volume.
2. Price Determination Phase:
The auction price is the price with the maximum executable volume. Additionally the minimum surplus, the market pressure and, if necessary, the reference price are taken into account when establishing the auction price."
Call phase seems to be 6 minutes and price determination split into two 2 minutes.