Why is it always six o'clock for the Hatter?

In the book, Alice's Adventures in Wonderland, the Hatter explains that he has annoyed Time, who he describes as a 'him' rather than an 'it'. He says that if you stay on good terms with him, he'll do whatever you like with the clock, such as arranging things so that, at the moment you had to go to school, he could make it so it's the afternoon and already time for lunch.

He goes on to explain that he was singing a song at a concert given for the Queen of Hearts when she cried out, "He's murdering the time!" This upset Time, who will no longer do anything the Hatter asks and has arranged things so that it is always six o'clock (and therefore always tea time.)

Alice sighed wearily. I think you might do something better with the time,' she said, than waste it in asking riddles that have no answers.'

If you knew Time as well as I do,' said the Hatter, you wouldn't talk about wasting IT. It's HIM...Now, if you only kept on good terms with him, he'd do almost anything you liked with the clock. For instance, suppose it were nine o'clock in the morning, just time to begin lessons: you'd only have to whisper a hint to Time, and round goes the clock in a twinkling! Half-past one, time for dinner!...We quarrelled last March...it was at the great concert given by the Queen of Hearts, and I had to sing "Twinkle, twinkle, little bat! How I wonder what you're at!"...Well, I'd hardly finished the first verse,' said the Hatter, when the Queen jumped up and bawled out, "He's murdering the time! Off with his head!"'

How dreadfully savage!' exclaimed Alice.

And ever since that,' the Hatter went on in a mournful tone, he won't do a thing I ask! It's always six o'clock now.'

A bright idea came into Alice's head. Is that the reason so many tea-things are put out here?' she asked.

Yes, that's it,' said the Hatter with a sigh: it's always tea-time, and we've no time to wash the things between whiles.'