def time_to_str(time_min:str, time_max:str):
    """
    Replace ':' to '-' from the time variables.

    Parameters
    ----------
        time_min: str
            Time variable with ':'.
        time_max: str
            Time variable with ':'.

    Returns
    -------
        time_min_str: str
            Time variable with '-'.
        time_max_str: str
            Time varaible with '-'.
    """
    if time_min:
        time_min_str = time_min.replace(":", "-")
    else:
        time_min_str = time_min
    if time_max:
        time_max_str = time_max.replace(":", "-")
    else:
        time_max_str = time_max
    
    return time_min_str, time_max_str