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As soon as your node would start receiving blocks in real time (after initial sync) you would get an info about latency, something like:

3030177ms th_a       application.cpp:514           handle_block         ] Got 33 transactions on block 19056032 by gtg -- latency: 177 ms
3033119ms th_a       application.cpp:514           handle_block         ] Got 37 transactions on block 19056033 by riverhead -- latency: 119 ms
3036482ms th_a       application.cpp:514           handle_block         ] Got 40 transactions on block 19056034 by xeldal -- latency: 482 ms
3039615ms th_a       application.cpp:514           handle_block         ] Got 31 transactions on block 19056035 by thecryptodrive -- latency: 615 ms
3042122ms th_a       application.cpp:514           handle_block         ] Got 50 transactions on block 19056036 by smooth.witness -- latency: 122 ms