1)
Why did they come during the day? Murderers usually come at night!
1.
Malbim: They used to be Bnei ha'Bayis, so they knew when he sleeps in the afternoon.
2)
What is "Mishkav ha'Tzaharayim"?
1.
Targum Yonasan: The sleep of kings. Radak - i.e. it is the custom of kings to sleep in the afternoon.
