Nate had long since realised that human women didn't function like female wolves. He couldn't use his charm alone, and he couldn't expect her to accept what her instinct told her to do.
Also, he knew how much Lara valued anything related to affection. He couldn't just spend the rest of the day imagining her naked body and waiting for the night. He had to think about how to approach her.
In the end, he did create a plan. It was perfect in his mind, but he was grown-up enough not to expect it to flawlessly go through.
After dinner, Lara sent the pups to sleep early. They were going to school the day after, and they weren't expecting any move from Nate since he had been so calm for two days. They didn't know the danger and just reached their beds and fell asleep after their mommy kissed their head and talked with them a little.
Then, she could finally have some time for herself.