When Velcan is first a werewolf, there is a full moon.

A few days later in the movie, werewolf-Velcan attacks Van Helsing and Anna's carriage while they're racing through the woods.

After he bites Van Helsing and Dracula kidnaps Anna, Van Helsing asks Carl when the next full moon is. Carl says, "In three days."

Now just because they're in Transylvania doesn't mean they can defy the laws of astronomy.