Change duration field from an integer, to a duration

[PossibleLlama]

Is your feature request related to a problem? Please describe.
Given that the duration field is intended to be a time taken, build upon that to clearly be a time in minutes.

Describe the solution you'd like
The duration field within Work, being changed from an int to Time.Duration.

Additional context
When creating/editing, the parameter will still be an integer. This is then converted as number of minutes. Seconds and below are treated as 0's.