The RTC is like a watch.
You can look at the time once a day.
Then reset an internal timer.
Compare the desired alarm time with 'time now'
Should be fairly accurate.
You could have an early alarm, say 5 minutes before
Then poll the RTC till the exact time.
Then send.
Search for arduino rtc alarm.
To find how to do it.
Can you poll the Node-Red host for it's time?