/**
 * Converts milliseconds to a formatted time string (HH:mm:ss).
 *
 * @param milliseconds - The time in milliseconds.
 * @returns The formatted time string.
 */
export declare function millisecondsToTimeString(milliseconds: number): string;
/**
 * Converts a time string (HH:mm:ss) to milliseconds.
 *
 * @param timeString - The time string.
 * @returns The time in milliseconds.
 */
export declare function timeStringToMilliseconds(timeString: string): number;
/**
 * Adds a specified number of hours to a date.
 *
 * @param date - The original date.
 * @param hours - The number of hours to add.
 * @returns The new date.
 */
export declare function addHours(date: Date, hours: number): Date;
/**
 * Adds a specified number of minutes to a date.
 *
 * @param date - The original date.
 * @param minutes - The number of minutes to add.
 * @returns The new date.
 */
export declare function addMinutes(date: Date, minutes: number): Date;
/**
 * Adds a specified number of seconds to a date.
 *
 * @param date - The original date.
 * @param seconds - The number of seconds to add.
 * @returns The new date.
 */
export declare function addSeconds(date: Date, seconds: number): Date;
/**
 * Formats the difference between two dates as a human-readable string with customizable granularity.
 *
 * @param startDate - The start date.
 * @param endDate - The end date.
 * @param options - Optional settings to specify the level of detail (e.g., ['days', 'hours', 'minutes', 'seconds']).
 * @returns The formatted difference string.
 */
export declare function formatTimeDifference(startDate: Date, endDate: Date, options?: Array<'days' | 'hours' | 'minutes' | 'seconds'>): string;
/**
 * Formats a duration given in milliseconds as a human-readable string.
 *
 * @param duration - The duration in milliseconds.
 * @returns The formatted duration string.
 */
export declare function formatDuration(duration: number): string;
/**
 * Formats the given date as a human-readable "time ago" string.
 *
 * @param date - The date to format.
 * @returns The formatted "time ago" string.
 */
export declare function timeAgo(date: Date): string;