I was told by the fish guy In a local pet store that 3 days is long enough to cycle a tank. He had never heard of the nitrogen cycle and had worked there 3 years (he offered that info). This was at a large chain store too. I don't buy fish there.
20 gal hex: 3 X Guppy,6 X Chili Rasbora, 2 X Dwarf Cory Hasbrosus (soon to be 4), 1 X Female Betta Imbellis
20 gal tall:currently cycling, soon to be re-aquascaped