I've never thought it a good idea to worm chickens unless you have a positive faecal done by an avian vet, but it's a personal decision. Chickens can carry a small load of worms without issue, and many wormers out there are basically ineffective on most worms; sorry to say, Wazine is one of them. Most folks use Ivermec Eprinext cattle wormer.
There is ALWAYS a withdrawal period. Two weeks seems to be the minimum that most folks go by.
Ground raw pumkin seed will help keep worms at bay; however, it is not actually a "wormer" and will not kill a large load of worms. The best thing, really, is to have a faecal done by an avian vet to see if there is a worm overload and, if so, which type, so you can choose a wormer that's specific for that worm.
GOOD LUCK!!!