JavaScript Date coercing to string?

Im running into an issue and due to my unfamiliarity with dates im not sure what exactly is happening.

Right now I am importing a .json file like so:
import widget from "@fixtures/widget.json";

In the .json file I have a normal JSON object and a property I need to update thats similar to this:
"WidgetTime": "2023-01-01T12:12:10Z",

I need to update this for testing to the current date so I use a function like this:

export function addHoursToDate(hoursFromNow = 5) {
  return new Date(
    new Date().setTime(new Date().getTime() + hoursFromNow * 60 * 60 * 1000),
  );
}

This actually works fine by default, however when I assign it to the property I get an error with typescript:
widget.WidgetTime = addHoursToDate(timeFromNow)

I get an error saying:

Type ‘Date’ is not assignable to type ‘string’.

From my understanding New Date returns a Date type and calling just Date returns it as a string. However appending toString() onto the function causing it to fail (Because I guess what I need is a ISOString?)

Im not really sure what’s going on, as it works despite the error because my guess is JavaScript is coercing it to a ISOString? But im unsure how to properly fix the error.

Thanks