I imagine that once Opal completes the task she was formed to complete, that she... kind of forgets to do anything else productive and just kind of chills and does her own thing. A great example that supports this is when she was first formed in the series, 'Giant Woman'. She gets back to the temple and Garnet asks where the Heaven Beetle is. Opal doesn't have it, and she splits. But wasn't the mission to retrieve the Heaven Beetle? Yes, for Pearl and Amethyst. But for Opal, her task was to save Steven, which she did complete. Once Steven was safe, Opal simply went home. She didn't think about the Heaven Beetle the entire way home. It wasn't the mission/task she was formed for, so she didn't even think about doing it. Likewise, in 'Log Date 7 15 2', Opal is formed to pick up the drill head and move it, and that's all. After that, Opal disappears for the rest of the episode, and since the episode is a flashback, she may have actually disappeared for days. Who knows?