Unfortunately I can't go into detail about the internals of the review process as we don't publicly discuss how this system works. What I can say is that the CWS and review teams are actively working on several different changes to the review process to combat malicious extensions and unwanted software. Among those changes is the adoption of a more defensive approach to permissions and development practices that are consistently used by malicious actors.
Regarding the difference in review time between SingleFile and SingleFileZ, I can only say that each extension is different. Review taking 1 hour for SingleFile vs 7 days for SingleFileZ is an artifact of this process and within my expectations of the current review queues. That said, we're aware of developer frustration around 7 day and longer review times and considering options here. We also need to make changes to better set developer expectations here.
As for what you can do to reduce review times, the single biggest thing you can do is remove broad host access like <all_urls>, https://*/*, http://*/*, etc. SingleFileZ is currently using <all_urls> for content scripts. After poking around your extension a bit I'd recommend removing content scripts from your manifest, replacing the <active_tab> permission with activeTab, and dynamically injecting content scripts with chrome.tabs.executeScript() when the user activates your context menu entry, browser action, or keyboard shortcut. This should significantly reduce how long SingleFileZ submissions are in review.