To change object settings in an arena for offline play or for hosting a LAN session, click Options->Arena Setup->Objects->Object Settings on the clipboard menu. The arena objects are listed with their down times in minutes and their hardness. The hardness is how many 1,000 lb bombs it would take to destroy that object and keep it down for the duration of the down time.
The Load button loads the last saved object settings. The Save button saves t
he current object settings. For example, if a LAN host has the ship down time set to 60 minutes and players in his arena ask him to change it to two hours, the host can change the ship object setting and it will be effective in his arena. If the LAN host clicks the Save button, the next time he hosts an arena or clicks the Load button, the ship down time will be two hours. If the settings aren't saved, the next time he hosts an arena the down time will be 60 minutes.
Once an object setting has been changed, the effect won't take place until the next action happens on the object (a bomb drop or some other sort of damage). So if an object with a 60 minute down time is destroyed and the down time setting is changed to three hours, the object will still only stay down 60 minutes. The next time the object is destroyed, it will stay down three hours.