Limit new user registration by time of day?

[chaz7979]

Is there a mod or cronjob I can run to turn my new user registration on and off depending on the time of day? 99% of my visitors are in North America and 99% of my spam registrations happen overnight. If I could turn off new user registrations from 2am-6am EST I would cut out my only remaining spam while not affecting the rest of my typical users.