The typical answer is generally :
As Time only exists if change occurs > since God is supposedly changeless without the world, there are no prior moments of time in which He could have acted earlier.
It's not perfect but still, the question assumes that Time before creation had a definite length or "metric," but this is a metaphysical mistake. Prior to the act of creation, God exists in "unmetricated" or "metaphysical" time. Without physical objects, stars, or uniform laws of nature to function as a clock, there is no fact of the matter as to "how long" God existed before He created. And because there is no measurement of duration in that precreation moment, the question of why He didn't create "sooner" (even 5 minutes) is technically unintelligible.
If you get a bit deeper on this, given the Swinburne Causal Principle (efficient causes must be temporally prior to their effects), then Jehovah actually could not have created the universe any sooner than He did : At the single precreation moment, any effect God causally brings about must occur at a subsequent moment, so once He exercised His power to create, He brought about that second moment of time, which was the earliest possible moment for the universe to exist.
To compare :
Imagine you are in a room with no clocks, no sun, and nothing moving. You could sit there forever, and even though you are thinking thoughts one after another, you couldn't say if you’d been there for an hour or a billion years because there is nothing to measure time with.
Jehovah was like that before He made the world. He decided to make the universe because He wanted to, and He just picked a "starting point." It wasn't "too late" or "too early" because He hadn't invented clocks yet.