Engineer Trick - Core Reactor confusion?

[Viladin]

As the title states, I am a little confused at the wording on the Engineer's "Core Reactor" Engineer trick, Its wording I feel is a little unclear.

"The engineer optimizes the power output of the automaton’s core, letting it use the excess power to increase its abilities in other ways. It gains a number of charges equal to the engineer’s Intelligence modifier + half of his engineer level (minimum 1). These charges return automatically if not used for 8 consecutive hours. As a swift action, the engineer can command the automaton to use a swift action and expend a charge from its core reactor to gain one of the following benefits: one extra natural attack at its highest base attack bonus, a +4 dodge bonus to armor class, or increase its damage reduction by 2/—.

I understand how many uses I get, the action it takes, and the bonuses, but the "These charges return automatically if not used for 8 consecutive hours", and how long the bonus lasts is unclear or just plainly not stated.  Currently RAW I interpret it as If I spend a Charge as a swift action my Automaton gains one of the following bonuses until its changed, Extra attack at highest BAB, +4 Dodge bonus to AC, or Increase DR by 2/--.

Or does each charge only last until my next turn?

Sorry if its a stupid question or if its already asked/posted somewhere, I am new to these forums.

Lasts until your next turn. I'll indicate that in the ability now.