Wait for the NIC to be assigned an IP address, then wait for google's DNS to respond, and then sleep for rand(30,600), used like this `wait_for_network.sh && do_something`

wait_for_network.sh

#! /bin/bash
# This script checks that the interface is up, and that an internet connection is available
# It is based on code from http://askubuntu.com/questions/3299/how-to-run-cron-job-when-network-is-up
#
# Then it sleeps for a random number of seconds between 30 and 600.
# This is based on code from http://tldp.org/LDP/abs/html/randomvar.html
#
# Collated by @JonTheNiceGuy on 2015-10-15
# Fix from @p1r473 on 2023-05-17 with thanks!

function check_ipaddr
{
  # Here we look for an IP(v4|v6) address when doing ip addr
  # Note we're filtering out 127.0.0.1 and ::1/128 which are the "localhost" ip addresses
  # I'm also removing fe80: which is the "link local" prefix

  ip addr | \
  grep -v 127.0.0.1 | \
  grep -v '::1/128' | \
  grep -v 'inet6 fe80:' | \
  grep -E "inet [[:digit:]]+\.[[:digit:]]+\.[[:digit:]]+\.[[:digit:]]+|inet6" | \
  wc -l
}

function check_google
{
  netcat -z -w 5 8.8.8.8 53 && echo 1 || echo 0
}

until [ `check_ipaddr` -ge 1 ]; do
  sleep 2
done

until [ `check_google` -eq 1 ]; do
  sleep 2
done

sleep $((RANDOM%570+30))

until [ check_ipaddr -gt 1 ]; do

Should be changed to

until [ check_ipaddr -ge 1 ]; do

As its perfectly acceptable to have only 1 IP address.

Awesome, great spot, thanks for that @p1r473! Code fixed