Yes, seconds are related to the Earth rotating around the sun. Simplifying slightly, the normal definition of a day relates to how long for Earth to rotate on its axis until the same spot on the Earth points at the sun again.
Compare Mean solar day vs Stellar day vs Sideral day - the difference is less than 5 minutes or so.
I'm not the commenter, but yes, often trading firms record all order gateway traffic to from brokers or exchanges at the TCP/IP packet level, in what are referred to as "pcap files". Awkwardly low-level to work with, but it means you know for sure what you sent, not what your software thought it was sending!
Compare Mean solar day vs Stellar day vs Sideral day - the difference is less than 5 minutes or so.