My 20g took about 2 weeks to cycle. It was easy as hell, I was on hols for one of the weeks. All I did was dump about 3 sachets of tetra delica bloodworms in and my leftover fish food that the fish didn't like, and vac it up once it was cycled.
I recently bought some Stress Zyme purely by accident. I was in a hurry and meant to get Stress Coat but grabbed the wrong bottle. Since I had a new 2.5 gallon to cycle, I decided to try it. I really couldn't tell any difference in the cycling time of the other 2.5 gallon I had just finished cycling without any additives. They both were within about a day of each other in the time they took. Both were fishless cycles with ammonia.