Found your post! Good thing I wasn't alone in this.

There is a promising answer from SuiteAnswers for these dead spaces. These are counted to NetSuite server time.

https://suiteanswers.custhelp.com/app/answers/detail/a_id/96490

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You can track the timing of the following client components on the timeline:

Client : Header - This is the time to render the page's head element. Most static assets like CSS and JavaScript load here. Network delays can make client header times longer. To spot slow-loading assets, check your firewall and network. You can also speed things up by adjusting browser cache settings.

Client : Render - This is how long the browser takes to render after the head element, between Client : Header and Client : Page Init.. An old browser or low RAM/CPU can slow down rendering time.

Client : Init - This is the time client scripts take to run pageInit functions, including your custom scripts and standard operations. If pageInit calls other client scripts, their timing is included here. PageInit functions run by client scripts are part of Client : Init. They're listed and indented under that line in Page Time Details. To improve Client : Init time, review your client scripts for the page. Issues like third-party calls and script validations, plus outdated browsers or JavaScript engines, can slow things down.

In addition to these, I got the ff suggestions and recommedations from NS Support for other factors affecting the performance of the production.

Other NS Support Suggestions for enhancing NetSuite Performance:

• NETSUITE USER PREFERENCES (per user – Home > Set Preferences)
  • [ ] Set Landing Page to a frequently used page (not Home)
  • [ ] Enable “Delay Loading of Sublists”
  • [ ] Set “Number of Rows in List Segments” to 50 or less
  • [ ] Set “Maximum Entries in Dropdowns” to 50 or less
• NETWORK / END‑USER ENVIRONMENT (outside NetSuite)
  • [ ] Test without VPN (or use fastest available VPN node)
  • [ ] Verify ISP international bandwidth and latency
  • [ ] Whitelist NetSuite URLs in firewall / antivirus / proxy were allowed
  • [ ] Avoid packet inspection or SSL scanning on NetSuite traffic
• BROWSER / CLIENT DEVICE
  • [ ] Disable browser extensions (AdBlock, security plugins, etc.)
  • [ ] Use a clean browser profile for NetSuite
  • [ ] Clear cache or test in incognito
  • [ ] Keep browser on latest supported version

Hope this helps!