You want to know if updated lead/person record data will reflect changes to that data made while the lead was in a wait step. This is important to know, because values could affect the following flow steps. For example, if there is a choice in the send email flow step that is determined by those values.
When a lead/person enters a wait step, they are put on hold (within that campaign only) until the specified time. No email content is generated in preparation of them exiting the step. When the wait step ends, the lead/person moves on to the next step in the campaign flow. Any information that was updated while they were in the wait step will be reflected in the next step.