Briar cocked his head slightly, not understanding why she was apologizing. But he wasn't known to be very polite and preferred to be direct himself. If he wanted to know something, he asked, just like she had.
"Been comin' on for a couple weeks now. I'd say it felt like it changed 'bout four days ago." At the same time he felt like he wanted Tris to help him be sure. A weather witch would know it from that side the same way he knew it from the plants. He'd bet she'd say it had come even sooner, with the first warm winds.
He'd argue she was wrong and he remembered in times like this that he missed his foster sisters a lot.