The best way to open a brown hairy coconut, not a fresh green one (assuming you are right handed, I imagine that sinister people can reverse the instructions, but I've not tried it).
First image the coconut is a head, everything is related to this, so the visualization is important. The three holes are the eyes and mouth of the face. They naturally form an eyes/mouth thing. you'll see that it only really looks like a eyes/mouth one way up. stare into its eyes (this bit is not so important, but I like to do it).
Now hold it in your left palm, under its chin/where the neck would be, with the 3 holes in the coconut arranged like the eyes and mouth of a face looking out to the right, mouth below the eyes, with the hair pointing up. There will be a slight 'seam' running between the eyes and back over the top of the head.
Then take a large, heavy knife and using the FLAT side of the knife (not the sharp edge), a meat cleaver works best, strike the coconut hard across the coconut's 'forehead', where its hair line would be, aiming to impact exactly on the 'seam'. You might need a few goes to get the crack right open, but sometimes it can be done in a single strike.
Get this right and it will crack in a straight line from ear to ear along the hair line. Works a treat. And usually you can use the shell for something as you get a clean break.
Once you have the first crack you can either prise apart or rotate the coconut in your hand and hit it a couple more times on the uncracked parts, following the same line as the first crack, to completely separate the two pieces.
Alternatively you can stick it into the oven for 15 mins, @400F, after which the shell should have started to crack. Then you can use the tool of choice to finish the cracking, rolling pin, hammer, wrench, flat of knife another coconut, whatever. But where is the fun in that?
There are 2 ways of looking at it; how long it will be safe to eat (ie from food poisoning) and how long it will still be appetizing and taste alright (ie not gone rancid).
As you've taken it from the tin it won't get that tinny flavour but as time goes on may absorb other flavours from the fridge so make sure you keep it away from anything that is strongly smelling. Also as around 87% of the coconut milk is fats it will soon go rancid, so keep that in mind, (you'll know when it does by giving it a quick sniff).
In terms of food safety, if it's UHT which most are, then it could probably last for a long time (as long as UHT milk) so about 2 1/2 weeks I'd say. Otherwise if it's not UHT then not as long. I would say about the same time as fresh milk so around a week as it contains sugars and fats and so is a very compelling proposition for any bacteria.
Other sites discussing this: http://community.cookinglight.com/showthread.php?t=14563, http://chowhound.chow.com/topics/291163 and http://forums.lowcarber.org/archive/index.php/t-418419.html.
Hope this helps!
Best Answer
Coconut cream, being generally oily, will give out rancidity in taste and smell once it rots. When extracted fresh as done in asia, coconut cream typically expires in a matter of hours. Since yours is canned, it's likely to have been reconstituted from coconut powder, ridding it from the spoiling enzymes in fresh coconut.
As long as you open your cans cold and keep its leftovers cold thereafter, it's easy to beat the printed expiry. The thing with coconut cream and liquid, it rots so suddenly, as soon as you turn your back. So its manufacturers are wary of users who aren't familiar with how sudden these things rot, which is why asians press and cook them within the same few hours.