PubNub's goal is to deliver messages, end-to-end, within 1/10th of a second (100ms) and we advertise that our global average (across all customers, end users, networks around the world) is < 1/4 second (< 250ms). 

The vast majority of delivery time is spent within the connections between the devices and the PubNub Networks (outside of PubNub's network) which means it really has mostly to do with the connection that the device has to the internet and the ISP's influence on the latency as well as distance from the PubNub PoP (point of presence, aka data center). Therefore, PubNub adds points of presence to best serve our customer base to achieve optimal performance. 

You can see for yourself PubNub's recent and historical performance stats as reported by Pingdom, including uptime and latency.