I suggest you read the transcript to the Good Eats show on freezing, or, better yet, find a copy of the episode to watch. (Good Eats is an American TV show focusing on food science.) Here are some relevant excerpts:
[In the freezer,] any present bacteria are going to have a devil of a time finding the moisture they require to live, breed, survive. Since they themselves contain a considerable dose of H2O, freezing halts bacterial activity altogether, though some of the little beasties can survive to decompose another day. While it is in this frozen state, the meat will remain unspoiled for years. But there's a problem. You see, home freezers work very slowly. That means that as those little H2Os start to line up inside, they'll create huge, sharp, jagged crystals that will rise up, slicing and dicing their way through cell walls, muscle fibers, and pretty much anything else that gets in the way. Now while frozen, you won't notice this damage. But when it comes time to thaw, all of those perforated cells will start to leak out moisture all over the place. It's called drip loss and it's not a sign of good eats.
Therefore, if you are buying the meat fresh (i.e., it is not already frozen), then you need to take special care in how you freeze it:
One good way to prevent drip loss is to freeze the target food very, very quickly to a very, very low temperature. So that instead of creating huge, jagged, nasty ice crystals, you get very, very tiny little ice crystals.
The episode goes on to describe a process for freezing meats at home (basically, the idea is to use small pieces of meat, freeze them separately on a sheet tray, and then once they are frozen transfer them to a bag for long-term storage).
Even though the meat will technically be safe to eat for years, there are a few caveats. For one thing, the environment in the freezer is very dry. That can cause moisture on the surface of the meats to sublimate and form ice crystals, otherwise known as freezer burn. This can be avoided by packaging the meat in a vacuum (e.g., vacuum sealed bags), however, if you don't have a good vacuum sealer, I would suggest limiting their freezing to 6 or 8 months in order to avoid freezer burn. Another reason to make sure you use an air-tight container is that fats are very good at picking up flavors of other items you might have in the freezer.
I am fairly certain the "fats will surely go bad" claim is a myth, especially since fat alone is a good preservative. Perhaps you should ask that question on Skeptics.SE.
Your proposed method is possibly dangerous, you'd be warming it enough for botulism to thrive, but not enough to kill it. When you cook it, cook it properly and all at once. What I'd suggest is simply cooking it on Friday, then re-heating it saturday, or getting up early enough to cook it through on Saturday. As for when to thaw it if it's a truly heroic size I'd thaw it in the fridge starting 48 hours before you want to cook it.
As for how long I'd usually do 20 minutes per pound plus 20 minutes as long as the meat is room temperature to start with, so for 7.5 lbs, so that's near enough 3 hours as makes little difference. Not that long really, if you wanted to serve at 1pm you'd want to get it out of the fridge as early in the day as you can, get the oven on at 8:40 on 350F (375 F on a conventional oven), get the meat in at 9, roast till 12, then rest it for an hour. Crank the oven up to max for the last 20 minutes to get the crackling extra crispy.
Best Answer
It should be healthy for now (assuming it was still relatively fresh when you put it into the freezer) but will actually break down faster now that you have frozen and thawed it. It will also have a much softer and significantly less pleasant texture than it did before, although that won't have much effect on blending.
When you freeze foods, the water in the food forms ice crystals, which are very sharp and which puncture the cell walls of the frozen food. These punctures cause the cells to lose a lot of water when the food is thawed and their water becomes liquid again. You will probably notice that your cantaloupe will look somewhat translucent and will have a lot of juice in the bottom of its container. This is due to cell damage and water loss post-freezing.
In fruits and vegetables, cell walls provide the structure that forms the fruit's texture, and damaging these walls will significantly weaken that structure. So the cantaloupe will be less firm and a lot less pleasant to eat on its own. It's probably still safe for now, but puncturing the cell walls will also make it easier for stray bacteria to get to the food's sugars and start multiplying, resulting in faster spoilage.
I would recommend using this immediately; failing that, 3 days maximum in the fridge would be as far as I'd go. If you want to do this in future, just leave the cantaloupe in the freezer until you're ready to use. Assuming it's tightly sealed to avoid freezer burn, it will keep for up to 6 months there.