I saw it as someone making the observation that there are exactly 315,360,000 seconds in a decade (not taking leap years into consideration). Then he goes on to calculate the seconds in decades that contain two leap years and then three. In that way, he is talking about both seconds and decades.
Actually, I just asked Google how many seconds are in a decade. :)
Esperanto is a really odd hodgepodge of various languages, and it's not quite as easy to learn as I thought it would be. I do think it's worth learning, though. This TED Talk is what finally convinced me to start studying it:
"Og år-" is essentially two "o" sounds back to back ("o" and "å" are very close to the same vowel) with a stop ("g") between them. The "g" really isn't voiced. Also, just like in English, pronouns are generally of less importance in normal speech, and therefore are unstressed compared to surrounding words.