Google Translate again:
But for, as you were saying, Epicurus denies that the length of time contributes anything to living happily, nor that less pleasure is perceived in the shortness of time than if it were eternal.
I wanted to break this down:
Epicurus denies that:
1. the length of time contributes anything to living happily
I believe that I could agree with this if it's an accurate translation. You can live a "happy" short life or a "happy" long life. The length of the life doesn't necessarily equate to one's overall happiness.
2. less pleasure is perceived in the shortness of time than if it were eternal.
This again hinges on the impossibility of eternal pleasure. Pleasure, as Cicero conceives of it, is by definition fleeting. He appears to imagine an infinite and eternal banquet. That's not the pleasure Epicurus is working with. It seems to me that "Torquatus" and Cicero are talking past each other, with Cicero of course being the author of the conversation. He's deliberately interpreting Epicurus and Plato via Philebus for his own ends.