I would have the poster mounted to a substrate before attaching it to the frame. foamcore is a good choice if the poster is not valuable. Acid free materials are worth the extra money if they are in contact with the poster. If you mount the paper poster to the wood frame it will never look very good. It will show the frame elements through the paper and the glue will cause differential shrinkage and buckling. If this is just a digital print that could be replaced this is what I would do; mount the poster to foamcore with spray adhesive taking care to avoid wrinkles. Mount the foamcore to your wood frame with double stick foam tape around the entire frame including cross pieces. This will keep the poster from showing the frame members though the paper and will Make an attractive presentation for a year or two. If you value the poster as an artwork, it is irreplaceable, have it done by a professional framer with good materials.
Open Time*
The amount of time the adhesive should be left to set, before it is covered.
If you're gluing two sticks together, with an adhesive with 30 seconds open time. You should apply the glue to one stick, then wait at least 30 seconds before affixing the second stick.
The amount of time the adhesive can be left before it is covered.
If you're gluing two sticks together, with an adhesive with 30 seconds open time. You should apply the glue to one stick, and affix the second stick before 30 seconds has elapsed.
Working Time
The amount of time from when the adhesive has set, to the time it will no longer bond.
Again gluing two sticks together, this time with an adhesive with a 5 minute working time. Once you apply the glue to the first stick, you have to affix and position the second stick in less than 5 minutes. If you don't affix the sticks within this time, the adhesive will not bond (or at least is not guaranteed to bond).
Set Time
The amount of time the adhesive needs to form a good bond.
Back to the sticks, this time with an adhesive with a 10 minute set time. Now that the sticks are affixed, you'll have to wait 10 minutes before they are adequately stuck together.
Pot Life
The amount of time an adhesive can remain viable after being mixed.
If you're gluing the sticks using a 2 part epoxy, with a pot life of 2 hours. Once you mix the epoxy, you have 2 hours to use it before it becomes useless.
Notes
*Some manufacturers use open time, and working time interchangeably. Open time should only be assumed to be different than working time, when working with adhesives that need to activate or set before being usable.
After doing more research, it appears there really isn't a set vocabulary used throughout the industry. Your best bet would be to contact the manufacturer, and ask them what they mean.
Best Answer
I believe you're looking to repair the plastic trim piece. For that, I would suggest a model cement that would be available at your local big-box retailer (like Walmart, but, since you're in Aus - Bunnings is Aus only, right? - I would hope you don't have those there), or at a hobby shop.
The good model cements will actually slightly dissolve the plastic at the broken edges, then when the solvent evaporates (in a couple of seconds), the plastic will meld together into one solid piece. You're not actually gluing them together, you are, effectively, welding them together. You'll have a nice strong bond, and if done carefully, you won't even see the crack. If you use something like this, you may not even have to get the trim ring off the light, just squeeze the crack together tightly, apply the cement with a cheap, disposable, fine-point brush, and hold it for 5 seconds or so. This type of model cement is going to cost a bit more, but it will make a nearly invisible repair.
If you can't find that (or don't want to pop for the cost), a "regular" type of model cement (for example, Testors™ is the brand I'm most familiar with from my youth) will work as a glue. I'd suggest that you get the trim ring off the fixture and apply the glue from the back. Use it sparingly - it will take quite a bit less than you'd expect - applied to the crack from the hidden side because it can leave a bit of a mess.
Once you've got the repair made, you have, essentially, nothing but the original plastic trim ring, so there's really no need to worry about heat resistance. If the original plastic was sufficiently heat-resistant, the repaired plastic will be, too.
If, for some reason, either of these glues don't hold it, you'll have to track down the actual brand of your fan and look for docs online to see if they indicate exactly what kind of plastic it's made of so you can get a compatible adhesive. However, I really think that some model cement will do the job for you just fine.