How to compare current time with previous time using DS3231 RTC

Projects Programming
1

I want to use a DS3231 RTC with an Arduino Uno to control a relay. I want to turn a relay on and after 15 minutes has passed turn it off. This will happen once per hour over a period of 14 hours. It's not important that the cycle begins on the hour, only that it turns on and 15 minutes later turns off and 45 minutes later turns back on. This cycle repeats over 14 hours.

I want to use an if statement to compare the TimeOn with the current time to determine if 15 minutes has passed. I know how to read the current time but I don't know how to write the code equivalent to: if currentTime => TimeOn + 15 min. Much appreciate any help.

2

Using the current time in seconds after midnight, you can turn on the relay at different times.
When it is time to turn on the relay, do so, then start a timer for 60*15 seconds.
When the timer ends turn off the relay.