RE: can I mix 5 min with 30 min?
There are several problems with using a microwave to accelerate epoxy curing: One is that there is no way to evenly heat the mixture and control the temperature of the cure and two the fumes that are emitted by the epoxy pose a distinct health problem when inhaled. People tend to build an intolerance to it over time much as they do with prolonged exposure to the fumes from CA glues, especially the thinner, more active types.
When I used to work at a major computer manufacturer in the mid-hudson valley that is known by three letters and associated with the color blue, we used an industrial type of epoxy for bonding the motherboards to the stiffener frames used to mount in the mainframe cages. These boards would be placed under pressure in an oven and stay there for several hours to accelerate the curing process. Those ovens were vented through exhaust filters and the temperature was controlled. We used to do oven profiles to ensure there were no excessively hot or cold spots in the ovens. The point is, the temperature we picked was not one we made up, it was specified by the epoxy manufacturer just for that one particular type of epoxy.
So if you don't know what the recommended temperature is to speed up the process, it's best to let it cure at the recommended room temperature specs so you don't get the brittleness or whatever. If you need it to set faster, use a faster setting epoxy. That's not to say that if the bottle is cold, you can't place it in a pot of warm water to bring it up a few degrees to where it should be (most are to be used at room temperature, 70 degrees fahrenheit or a bit more).