Calling len(ddf) within the 01_datraframe.ipynb tutorial fails due to mismatched dtypes.

**Describe the issue**: Calling len(ddf) within the 01_datraframe.ipynb tutorial fails due to mismatched dtypes. CRSElapsedTime needs to be a float and TailNum needs to be a string.

**Minimal Complete Verifiable Example**:

Within the notebook, execute this cell:

```python
# load and count number of rows
len(ddf)
```

**Anything else we need to know?**: This actually addressed a few cells down in the explanation of why calling .tail() fails. Perhaps the fix is as simple as moving the len() cells after the tail() cells.

**Environment**:

- Dask version: 2023.8.1
- Python version: 3.11.4
- Operating System: Windows 11 Enterprise 22H2 (22621.2134)
- Install method (conda, pip, source): Dependencies from pip. Notebook cloned from GitHub.