Peak time is 8am - Midnight. Basically that means that any usage between those times counts toward the 120GB limit, whereas anything downloaded between midnight and 8am doesn't (free usage overnight, basically).
I thought I should pop in here and clarifying the product refresh rumours.
At the moment we are working on a refresh of our product set, but this is in the very early stages and to set your expectations on it, there aren't going to be any changes in the short term. The refresh is likely to be happening later in the year. Sorry if this isn't what you wanted to hear but rest assured we are looking at it and taking your feedback on board.