I noticed that when one of the devices being monitored in Cisco Prime 4.2 went down, it did not appear as "red" immediately on the Topology Services map. It appeared s red maybe after 30 mins or so. Can you help me adjust this?
The topology services map is not designed to display real time status.
By default, LMS polls the entire network every 4 hours (in LMS 4.2, used to be every 2 hours) and updates the topology display based on that. You can add a subset of you devices in the Critical Device poller for more frequent checks but it is resource-intensive and not recommended for more than about 30 devices in total. (Reference)
The Fault and Event viewers can also be used for better visibility of device faults.