My Exciting Scene

The text says

"Jonah had nervous tremors in his stomach. The hand holding the Elucidator was shaking. He wasn't even sure what he was asking for. But he couldn't stop now."

"You have to let us try," Jonah argued. "Let us try to save Alex and Chip and time. Or else..." He had to come up with a good threat. Or else what? Oh. "Or else we'll do our best to mess up time even worse than Hodge and Gary did."

"so what"

Jonah is very nervous and not sure of himself or why he told JB that him and Katherine had to go with Chip and Alex to the 15th century. Why he had told JB that they could fix 15th century and how they would do it

Jonah is really trying to convince JB that he and Katherine are serious, and that they really want to help Chip and Alex be able to come back to their time. To do so Jonah comes up with a threat that he thinks will defiantly convince him to let them fix time.

"Jonah's stomach gurgled. He could tell that he was out of the nontime limbo because he was hungry agian. Starving, in fact.
Jonah is hungry for food that he has not had in a long time and probably has high hopes that there is good food in the 15th century.