'in the moment' in a sentence without the preposition 'in' possible?

The author of this sentence chose to leave out the preposition 'in' before the phrase 'in the moment' which kind of throws me off. I can't make friends with it.Is there are rule behind it? 

I always dreamed that I would own an amazing animal like this someday; a huge teddy bear that can wrestle playfully with children one moment and in the next, snap to attention at the owner's command and be the protector