What is the proper way to express a length of time in TypeScript?

I am currently creating an interface for a personal project and need to include a field that contains a length of time that a task took to complete. What is the proper data type/format for expressing a length of time in TypeScript?

Here is my interface

export interface Task {
    id: number, 
    name: string,
    taskDate: Date,
    taskDuration: {DURATION TYPE HERE}
}

I’ve seen several ways online to calculate a duration from 2 dates, so I could just use a taskStart and taskEnd and then calculate from there, but surely there is a way to simply enter a duration without having to perform a calculation.

>Solution :

ISO 8601 specifies a format for durations, which is pretty much industry standard.

Some examples:

P1D - one day
PT5H - 5 hours
P2YT2S - 2 years, 2 seconds

https://en.wikipedia.org/wiki/ISO_8601#Durations