Perfect time synchronization over a network with unknown latency is provably impossible.
Fairly certain distributed physics experiments will be using atomic clocks that are not synchronized over the network. And/or they'll use direct satellite or GPS time sources which have predictable latencies.
CERN at least seems to be using a solution that is running over Ethernet[1] but with custom hardware that is probably fairly expensive. They use a single time source and then measure the delay between each switch/node.
Though, this is limited by needing to be able to run a cable between each node so idk how your definition of a distributed experiment fits.
Fairly certain distributed physics experiments will be using atomic clocks that are not synchronized over the network. And/or they'll use direct satellite or GPS time sources which have predictable latencies.