Night would be excellent. The city folk will be tired, better to scare, makes it more dramatic when there are fires. I don't see how monsters lose by attacking during the night. I personally would love to burrow up to the temple and start off by disintegrating some significant piece of it.
Which is definitely something I'm considering. I'm a powerhouse with my natural attacks, true, but unburrowing to let lose fire or destruction and slipping into the ground is a great way to split their forces and send them chasing frantically. I can disappear underground, removing some portion from the fight, to emerge where I please (probably undetected) breathing away again.