The note came eight hours into Neville's shift, but he didn't receive it until three hours later when he finally made it back into the office. He and Ron had been tracking down an illegal shipment of potions supplies, and finally gotten the lead they needed to put the case to rest.
He was exhausted, and a little beat up from the duel that had ensued when they'd finally caught the smugglers, he felt what little was left of his strength desert him as he read the letter. Matt was missing.
He glanced at the clock. Matt would have taken lunch at noon, which meant that by three he'd have been missing for three hours. It was now nearly seven, which made it six hours and since there was no additional message he had to assume that Matt was still missing.
Writing a quick note back, he Apparated home. "Matt?" He called out, trying not to panic. Maybe he'd just fallen asleep. Merlin knew Matt was exhausted after what had happened at St. Mungo's. However, there was no answer, and Neville had to admit the worst.