If your end device has ICMP, then you could change the alert rule to act on that instead of SNMP for device down. False positive device down - LibreNMS 1.38-48-gfbbc257
Or, you could increase the alert “delay” to 6m, to cover 2 x SNMP polls, which should greatly decrease false positives.
Not sure on the other question, but i know OpsGenie and other transports have smart features, such as “If not acknowledged in 5 minutes, and after 5pm, ring my mobile” etc which ties into the LibreNMS acknowledgments i think.