Thanks for your comment and feedback!
There are at least 2 pixels difference between the void and newly placed orbs. This is intended. I’m not quite sure if I got your point, though.
Actually, it is possible to survive on NORMAL for more than 3 minutes. Note that you can place orbs while the void approaches. However, you cannot have more than 15 orbs at the same time. So to place a new orb, you will need to wait until an orb breaks.
Placing your orbs very close to the void means that they break sooner and therefore you can place new orbs sooner. Utilizing this can help you place 40 or even more orbs during the game.
On the game page are more tips like this.
Also the “difficulties” are more like different “game modes”. I’m sorry that I didn’t communicate that well. That is why I think about renaming NORMAL and HARD to make clearer that those are not difficulties.