This article explains how the behavior of BMP changes, when System Clocks changes from default value

Almost every BMP packet carries the 'current' time, it's a little bit expensive to query the real time while generating the packet.

That's why BMP set a base time as a "wall clock" during the initialization.

If the NTP time changes, BMP may sticks with the 'old' time, until the bounce of the BMP session. However, BMP should update with the new base time whenever the system clock has changed. Our Engineering is working on this to fix this through PR 1787582

Root Cause:

When the system time on a router changes, via manually or NTP adjusting, BMP packet might carries wrong timestamp based on the old system time. It will last until BMP session is torn down and established again. This system time changing situation should be rare in the real network.

Workaround

User can make the system time change before bring up BMP sessions, or bounce the BMP session after the system time change. This will reset the BMP base time for each BMP packet.

External-Trigger

System time changes when BMP session is already up.