It's difficult to answer accurately as there is different versions of cron with potentially varying accuracy.
NTP will definitively be a must for a solution like this, and use ntpd instead of ntpdate, as ntpd will constantly adjust the "length of a second" to the correct length of a second as opposed to ntpdate which just sets the time and allows it to drift again. Once a system has booted, it no longer uses the battery backed RTC clock, but will use CPU generated interrupts instead which are much more accurate, but might need to be adjusted slightly.
On to cron:
From the man page of cron:
cron then wakes up every minute, examining all stored crontabs,
checking each command to see if it should be run in the current
minute. When executing commands, any
output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab, if such
exists). The children copies of cron run‐
ning these processes have their name coerced to uppercase, as will be seen in the syslog and ps output.
Unless cron wakes up every minute on the minute, you have no gurantee for secondly accuracy, but I'd recommend not to take this for granted and put it to the test.
Synchronize the servers using NTP, schedule a cron job to touch files over a period of time and stat them.
After you've touched enough files you should be able to get an idea of what kind of accuracy your cron has.
If your application absolutely has to synchronously within the second, or if your cron is too inaccurate, it will be better to start the scripts a few seconds early and using your NTP synchronized clock, have the scripts wait for the right moment in time to proceed with your request.
Edit: A quick bash script to sleep until the specified minute:
minutes_to_wait=`echo $minute_to_start - $minute_now -1 | bc -l`
to_sleep=`echo 60 - $now + \( $minutes_to_wait \* 60 \) | bc -l`
You can run it in cron like:
29 7 * * * /path/to/above/script.sh 30 'the real script'
And the job will start at 07:30:00
In my testing it drifted within 10-20 milliseconds, and it doesn't work if you want to start at X:00:00.00 (on the hour), so not something I'd actually use in production.