If you can find out the IP address of their server, just ping it and it will give you the result
64 bytes from 66.102.9.105: icmp_seq=0 ttl=55 time=38.663 ms
64 bytes from 66.102.9.105: icmp_seq=1 ttl=55 time=37.426 ms
64 bytes from 66.102.9.105: icmp_seq=2 ttl=55 time=36.512 ms
64 bytes from 66.102.9.105: icmp_seq=3 ttl=55 time=36.923 ms
64 bytes from 66.102.9.105: icmp_seq=4 ttl=55 time=36.298 ms
64 bytes from 66.102.9.105: icmp_seq=5 ttl=55 time=36.967 ms
64 bytes from 66.102.9.105: icmp_seq=6 ttl=55 time=37.900 ms
64 bytes from 66.102.9.105: icmp_seq=7 ttl=55 time=36.492 ms
TBH it depends how you're trading as to what value you need. Making sure its not too variable is important as well (commonly called jitter). The banks in the city doing algo stuff all want 1-5 ms