Maintenance for the week of April 20:
• NA megaservers for patch maintenance – April 20, 3:00AM EDT (7:00 UTC) - 12:00PM EDT (16:00 UTC)
• EU megaservers for patch maintenance – April 20, 7:00 UTC (3:00AM EDT) - 17:00 UTC (12:00PM EDT)
Pretty sure I've seen werewolves during the day too in Grahtwood.
Those are not the kind that can infect you. Only werewolved/bloodfiends in The Rift, Bangkorai and Reaper's March can infect players.
Any other WW/vamps (and there are a lot in Glenumbra/Rivenspire) are story related.
ForgottenHeretic, I think it was true in the beginning, and they may still have a better chance of spawning during the right moon phase, but I think ZOS tweaked it because of people camping the spawn sites and killing them.