You generally convert to a duration from either a sys-time or a naive-time. The precision of the input is retained in the returned duration.

To round an existing duration to another precision, see `duration_floor()`

.

## Examples

```
x <- as_sys_time(year_month_day(2019, 01, 01))
# The number of days since 1970-01-01 UTC
as_duration(x)
#> <duration<day>[1]>
#> [1] 17897
x <- x + duration_seconds(1)
x
#> <time_point<sys><second>[1]>
#> [1] "2019-01-01T00:00:01"
# The number of seconds since 1970-01-01 00:00:00 UTC
as_duration(x)
#> <duration<second>[1]>
#> [1] 1546300801
```