There was no time behind the mask. Minutes became hours, hours became days, days became weeks, and before he realized it, years would pass. The monotony of his breathing, the red glare of his viewscreen: they just enhanced the feeling of sameness, of timelessness. He would not have known any time had passed at all, had his Master not reminded him.
Everyone of his lifedays was remembered with ceremony, in delibrate contrast to the Jedi, who had barely acknowledged them. Every anniversery of the birth of the Empire was a day of celebration, even if he would have preferred to declare the day a day of mourning. And so every year, he was reminded of what he was, and what he was not.
He was not a father. The first Empire Day he spent deep in thought about a little girl with Padme's eyes and his features, toddling along with a smile on her fact. Her first word, in his mind, had been 'Dada'; a corruption of 'Daddy', not 'Darth'. His Master had to order him to report to the ceremonies in the Imperial Palace, and afterward, he had spent hours destroying droids and furniture in his mingled grief and rage.
He was not a husband. On his twenty-eighth lifeday, his Master took special pleasure in reminding him that he was now the same age as Padme, the age Padme would be for eternity. That day was the first time he seriously tried to kill the old man: not for his power, but to stop the gloating and the cackling that his Master insisted on.
He was not a Jedi. On the tenth Empire Day, the Jedi were officially declared eradicated. His Master praised him in the Great Imperial Square, in front of thousands of holocams. No one understood the deep irony in the last of the Jedi being praised for destroying his brethren. When the ceremony was over, he spent an hour in his meditation chamber torn between laughter and rage.
He was not a man. By his fortieth lifeday, he had divorced himself from all the weaknesses of the past that had plagued him. He was no more than a machine, a weapon, a hyper-intelligent droid. Sometimes he thought he was successor to the long-forgotten General Grevious, who had preceded him in the position of half-mechanical terror of the galaxy.
What he was, though, was a man outside of time, with only the metronomic hiss of his respirator to tell him any time had passed at all.