You should never trim them in winter, as these plants can be very sensitive to cold. During the big freeze of 2007, I lost a fairly big one, although it's usually the little ones that are killed by frost. And you shouldn't trim them in summer, as they're doing the best they can to survive in the heat, and besides, it's not wise to be out in 100+ heat, yourself!
I've had Phoenix roebeleniis, which is their Latin name, here at The Tropical Paradise for over twenty years. And I trim them back as far as I want, and they grow back looking better all of the time. By the way, if you're wondering what those pods are, they're the beginning of the flowering stage of the plant. Personally, I let them completely flower and then snip them off. If you cut the pods too soon, I've discovered, they get real messy, and they keep growing anyway.
As you can see in the photo, I just trimmed a few minutes ago. Oddly enough, the stubs keep growing, so I like to go back later and snip them down again. The plant in the photo has been in the ground for about twelve years and was planted as a 5-gallon. The trunk is about four feet tall, which makes it a big miniature. The biggest I've ever seen these grow is twelve feet, and that's a real big miniature! If I had planted a full-sized palm tree there twelve years ago, all I would see would be a telephone pole, and it would expensive to remove. I like my pygmy date palms!