public Builder<T> setChronoUnit(final ChronoUnit chronoUnit) {
            this.chronoUnit = chronoUnit;
            return this;
        }
If the type of the property is a {@link Duration} this is used to indicate how the value is saved in the
database. For an example a Duration of one hour will be saved as "60" if the ChronoUnit is {@link ChronoUnit#MINUTES}, or
saved as "3600" if the ChronoUnit is {@link ChronoUnit#SECONDS}.
<p><strong>Important:</strong> The ChronoUnit is required, and must be set, if the type of property is a Duration.

@param chronoUnit the unit of time the Duration is saved to the database in
@return The current SystemProperty builder
xmppserver/src/main/java/org/jivesoftware/util/SystemProperty.java