shoot I use the 5 min all the time, its fine for gluing little parts, not large areas you just have to be prepared to use it quick and get the glue on the surface so it gets into the pores of the wood.
for the longer working time 30 min of course lets you work the area and adjust parts,I like using the faster setting adhesive on certain applications more of a personal preference if it didn't work then I think it wouldn't be manufactured ,
epoxy myth #1 more makes it stronger it just makes it heavier,if your going to strenthen a area and it is in a corner use wood to brace the area not more glue.
its lighter and adds structural strength
as for thinning epoxy pop the top and a quick zap in the microwave aprox. 5sec.on med. it thins the resin right out when it turns to a sludge in the bottom of the bottle,I will give it a zap and check to see if its melted swirl it around and zap it again if its not fully melted just remove the top so the air can vent whenever you heat a epoxy bottle,wheather you zap it or use the hot water method, they both work equally well the hot water is a bit slower is all.
then let it cool down and use it as you like.