fix #3477: blank timer when "show remaining duration" is enabled

[root-sarvesh]

Fixes #3477

Problem

When enabling “Show video remaining duration”, the video time display becomes a blank bubble.
Sometimes only the separator (/) remains visible.

This issue:

• Occurs on Firefox and Chrome
• Happens even when logged out
• Appears after a recent YouTube UI update
• Disappears when the setting is disabled and the page is refreshed

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Root Cause

YouTube’s updated player UI splits the timer into multiple elements:

• .ytp-time-current
• .ytp-time-separator
• .ytp-time-duration

The previous logic hid or replaced parts of this structure.
As a result, YouTube continued updating the timer internally, but the visible text nodes were missing, leaving a blank display.

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Solution

This fix preserves YouTube’s native timer structure instead of hiding elements.

Changes made:

• Cache the original duration text once using dataset
• Avoid modifying the current-time element (which YouTube updates every tick)
• Append the remaining time to the duration text only
• Keep YouTube’s separator and DOM layout intact
• Run updates within ImprovedTube’s existing player update loop

---

Result

The timer now renders correctly as:

1:27 / 5:42 (-04:15)

Tested on

• Firefox
• Chrome
• Logged in and logged out

[ImprovedTube]

hi @root-sarvesh
it seems some elements in appearance : player are duplicated? ; #3471 @dodieboy
thank you very much!

[dodieboy]

I don't think my previous PR caused the duplicate in appearance->player, but will double check later