Okay, here is how Sundial ticks. The card has two abilities, one static (creatures can't attack) and one activated (card draw). This is the first time a card with two abilities has come out in Elements, so naturally, it's going to have some quirks. Here's how they break down.
If you play Sundial, your creatures don't attack. Your opponent will not be able to attack on the following turn. Here is where it gets interesting. The following turn, Sundial's activated ability becomes available to use. For simplicity, I will refer to this as turn B. If you decline to draw a card from Sundial, your creatures will not attack, and neither will your opponents, and the following turn you can draw a card from sundial and it will disappear from play while letting your creatures attack. That is how Sundial is supposed to work.
However, there are other conditions that determine when creatures attack while Sundial is in play.
1.) If you draw a card from sundial on turn B, your creatures will not attack, but your opponent's will.
2.) If you draw a card from sundial on turn B, and draw a card through another permanent such as hourglass, your creatures will attack, as will your opponent's.
3.) If you draw a card from a non-sundial permanent on turn B and do not draw from sundial, your creatures will not attack, but your opponent's will.
I have tested many other situations to find a universal rule with sundial:
Every card you draw through an activated ability while sundial is in play shortens the stasis period by 0.5 turns. (1 full turn = your turn + opponent's turn)
If you have any other questions regarding sundial, just ask. This should clear up most of the confusion.