Make action happen after time is passed using interrupts
Since I don't have enough reputations to comment on your question I am going to drop my two cents here.

Since your question is a little bit vague, I am going to suppose that you don't want any external interrupts thus, you don't need to use the attachInterrupt function. I am going to suppose that there is no need to use timers' interrupts as well.

Have a look at the following code:

#include &lt;Time.h&gt;
#include &lt;TimeLib.h&gt;
#include &lt;Adafruit_RGBLCDShield.h&gt;
#include &lt;utility/Adafruit_MCP23017.h&gt;
Adafruit_RGBLCDShield lcd = Adafruit_RGBLCDShield();

void setup() {
  lcd.begin(16, 2);
  setTime(02, 10,00, 14, 03, 2016); 
}

void loop() {
  char time_out[16];
  lcd.setCursor(0, 1);
  sprintf(time_out, "%02u:%02u:%02u",hour(),minute(),second());//use %x to get hex 
  lcd.print(time_out);  

  int totalSeconds = (hour() * 3600) + (minute() * 60) + second();  
  lcd.print(totalSeconds);
  if(totalSeconds &gt; 7806) {
    blink();
  }
}

void blink() {
  lcd.print("time passed");
}


You should know the following:

Commands inside void loop() is going to be executed for ever again and again. Especially lcd.print(time_out);. You had better refresh the LCD every 1 second.

After 6 seconds blink() is going to be executed many times (maybe forever) since it is inside the loop and if(totalSeconds &gt; 7806) is going to be always true.

If you have any question let me know in the comment section.