20 to 26 is pretty much average for the majority of chickens and bantams. There is no precise date on egg laying. For worming info check out this: http://keeping-chickens.me.uk/what-to-keep-in-stock/flubenvet . The person writing this article does it twice a year as a preventative measure with flubenvet. Flubenvet is the main wormer on the market. Obviously how often you worm will depend on the brand and quantity you use.