[Bug] Elapsed time and ETA include queue waiting time

### Custom Node Testing

- [x] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

The elapsed time should start at 0s when execution actually begins.

For example:

Prompt #1
Queued → Execution starts → Elapsed: 0s → 1s → 2s → ...

Prompt #2
Queued → Waiting in queue → Execution starts → Elapsed: 0s → 1s → 2s → ...

The time spent waiting in the queue should not be included in the elapsed time or ETA.

### Actual Behavior

For the second and subsequent prompts, the elapsed time starts from when the prompt was queued rather than when execution begins.

For example:

Prompt #1
Queued → Execution starts → Elapsed: 0s → 1s → 2s → ...

Prompt #2
Queued → Waiting in queue → Execution starts → Elapsed: exceeds Prompt #1's execution time

This also causes the ETA to be incorrect because the queue waiting time is included in the calculation.

### Steps to Reproduce

1. Queue multiple prompts at once.
2. Wait for the first prompt to finish and the second prompt to start executing.
3. Observe the elapsed time and ETA of the second prompt.

### Other

The issue is especially noticeable when multiple prompts are queued at once, as the longer a prompt waits in the queue, the more inaccurate its displayed elapsed time and ETA become.

- ComfyUI: latest master
- Browser: Chrome
- Environment: Hugging Face Space

Reproduce the issue by queuing multiple prompts and compare the elapsed time and ETA when the second prompt starts. Trace where queue waiting and execution timing are recorded and displayed; done means elapsed time resets at execution start and the ETA excludes time spent waiting in the queue.

Written by the indexing model from the issue text.