Atlas understood that there was a chance that Lilith was safe and didn't need his help, but he didn't want to take a chance. He had been late once before. He didn't want to lose another person in a similar manner.
If there was even the slightest chance of Lilith being in danger, he wanted to be there for her.
At a time like this, when Lilith was missing, every hour was too much. Still, he gave Lancaster a chance. He gave them six hours to enter the city and to find Lilith.
"If you can't find her roaming on the streets safely in six hours, that will confirm that she is in danger," Atlas stated. "I will have to greet them personally to ask for Lilith's return."
"I understand. I promise that if I can't find Lilith in six hours, I won't stop you. Instead, I'll help you. Even I won't let anything happen to Lilith."