Yep, but it would be inadvisable to set it lower than the peer’s delayed ACK timeout, unless you want to just always resend every packet.

For a webserver won't that just be the default route most of the time? It's effectively a systemwide tune at that point.

The shorter timeout would likely be for downstream app servers in the same datacenter, not for the general internet. That is, adding a route for a specific network not because the default route doesn't work, but for tuning that setting only for that network.