The `DimCoord` constructor doesn't need NumPy arrays for `points` and `bounds`. It'll work quite happily with scalars, tuples, etc. So if you define `points` as a scalar (as would result from `points = units.date2num(valid_date)`) you could just do:
```
bounds = (points - field.period_minutes / 60.0, points)
```

That said, if you do make `points` a scalar, I'd recommend changing the name to just `point` to reflect that.