The column 'deduct period' gives you the option when the system should deduct the credits used for an event.
There are five options: disabled, 1, 7, 10 and 14 days. If you choose for disabled, the system reads it as directly. When you choose for 7 days, events further than 7 days ahead won't be charged directly, but they will be charged 7 days before the event starts. When the system is unable to charge credits you will receive an email.
You also can add a minimum of credits. If the client's credits are reduced to this amount, the client won't be able to use any more credits of this type. it is possible to use a negative amount here (e.g. -1 allows the user to have -1 credit of this type).