def get_false_times(obs_pair_hash, variable):
    """
    Get the timepoints where the variable is false.

    Parameters:
        obs_pair_hash: the dictionary containing all observations by time unit as a tuple (case, variable).
        variable: the observation to look for.
    
    Returns:
        A list with all timestamps where the observation is not present
    """
    results = []
    for key in obs_pair_hash:
        obs = [item for item in obs_pair_hash[key] if item[1] == variable]
        if len(obs) == 0:
            results.append(key)
    
    return(results)