Make more provided delay value formats work

Currently you have to provide the delay in exactly this format (or provide a Date):

```
1w 2d 3h 4m 5s
```

All of these are optional, so you can just pass one of them. But they need to use the correct letter.

We should make it so you can pass h, hr and hour for hours. Same for others, coercing values to the correct format.

If they can't be coerced then we should throw a good error.