I'd wait till you KNOW they are filming. xx

I usually send fan mail when they start filming. I have never tried when they weren't filming

I am planning on writing to two TV show sets, who just got renewed for there second seasons.
Im not sure if there filming them yet but, im assumeing its going to be sooon. but,

Do you think I should send the letters anyway and let them sit there until they start filming
or send them as soon as i know there filming?

Any suggestions?