Most exchange open/close auctions use time priority to deal with order imbalances. If there are buy orders for 300 shares and sell orders for 500 at the same pr

Most exchange open/close auctions use time priority to deal with order imbalances. If there are buy orders for 300 shares and sell orders for 500 at the same price, then only first 300 shares on the sell side will be filled. The speed incentive is a consequence of time priority, not the auction frequency. Switching from continuous auctions to open/close style auctions every 5 minutes would not remove the incentive to be fast.