“Joe,” I called, the moment I could open my mouth. “An army. There’s an army out there."
My beta reader is unsure about the comma after 'I called'. I think it should be included because 'I called the moment...' could throw the reader, if only for a second. However, he found the comma very jarring.
Should it be included or not?
Note: I looked at the help center, and I believe this question is on topic, as it is a specific question about a particular point in my text, as mentioned under 'How can I ask about checking my text?' However, if it's still off topic, just let me know.