30 Minute has more time to seep into the cracks and uneven parts of your wood, which would produce a stronger joint. 5 Minute is quicker and I have never had a joint fail on a plane and a wreck usually shows the glue joints all stayed together, it was the wood around them that gave up on impact. I usually use the 15 and 30 minute if I am putting something together and need more time to spread the glue. Good Luck, Dave