Deep thoughts while waiting for my tea to cool...
Bands named after days of the week: Happy Mondays, The Mondays, Tuesday, Wednesday, Thursday, The Saturdays, The Sundays and Taking Back Sunday.
Bands named after months: April Ethereal, Mayhem*, Death in June**, Texas in July, August Burns Red, Black September, October Tide, November's Doom, December.
Ergo, months are more metal than days. Especially if you add "death," "doom" or "black" to them [though, I guess that's the case with most things].
*Okay, you caught me. I couldn't think of any bands named after May. Sorry. Though I do wonder why there aren't any metal bands named after the coldest months. January's Doom? Black February? March Madness?
**Not metal, but way darker than a couple of folkies ought to be, and a huge influence on bands like Agalloch, Neurosis, Swans, etc.