as soon as the last round of shots has been completed you can start with longer walks. I would hold off until then because you don't want them to accidentaly pick anything up where other animals have walked before they are properly vaccinated
"There are two temptations to which people fall prey with dogs. The first is to think that biology counts for everything. The second is to think it counts for nothing"
- Tom Junod
“When you KNOW better you DO better.”
― Maya Angelou