Just an FYI - the 120 is very malty. Don't expect a big hop profile. It is quite good though.
It's hoppier than you think it is. They dry-hop it for months and it's well above 100 IBUs (the approximate limit of most people's ability to discern an increase in bitterness). But because it has that balancing malt, the bitterness is percieved differently. Same way that nobody realizes that the 90min is 90IBUs (+/- a little) and 9%ABV simply because it's so balanced.*
Duvel, for example, is only about 30 IBUs but because it's so dry, you think it's much more.
I'll "continuously hop" my pale ales, IPAs and such just during the last 15-20 minutes. Continuous hopping the whole time seems a bit wasteful, since boiling hops for more than 20 minutes takes away most of the flavor and aroma you'd get anyhow... and so why not use them during the full boil for maximum extraction?
I just take a handful of pellets and drop one or two in at a time for the 15-20 minutes. I also make sure to have the last of them in for at least 2 minutes because otherwise you're hardly getting anything out at all. If I want more aroma than that gets me, I'll dry-hop.
One last thing - If I'm going to "continuously hop" a beer, I generally try to stick with one type of hops for flavor and aroma (perhaps a different dry hop, though). This way you get a more "pure" profile and you get to see one hop do everything it can. Just my choice, but I like the results.
*EDIT: Forgot to add, DFH only brews 120min about twice a year. So depending upon when you buy it, that bottle can be pretty old. There's no worries about spoilage, of course, but the hop profile does mellow significantly with age. There are different opinions on whether you should cellar 120 or drink it fresh but I'm of the opinion that it's at its best with that very fresh, vibrant hop flavor and aroma. I've had it on tap at the brewpub and I think I certainly prefer that serving method best. Anyhow, just putting that out there.