feat(time): Convert Date into DateValue for intervals

src/time/fromDate.js

@@ -0,0 +1,15 @@
+import DateValue from './date-value';
+
+/**
+ * Convert a date into an object usable in the exported values.
+ */
+export default function fromDate(date) {
+	const result = new DateValue();
+	result.year = date.getFullYear();
+	result.month = date.getMonth();
+	result.day = date.getDate();
+	result.hour = date.getHours();
+	result.minute = date.getMinutes();
+	result.second = date.getSeconds();
+	return result;
+}

src/time/interval-value.js

@@ -1,9 +1,10 @@
 import { toStart, toEnd } from './intervals';
+import fromDate from './fromDate';
 
 export default class IntervalValue {
 	constructor(start, end) {
-		this.start = start;
-		this.end = end;
+		this.start = start instanceof Date ? fromDate(start) : start;
+		this.end = end instanceof Date ? fromDate(end) : end;
 	}
 
 	toStartDate() {