Compare tm’s

	struct tm Tm1 = {0};
	struct tm Tm2 = {0};

	strptime("2020-08-29 11:05:13", "%Y-%m-%d %H:%M:%S", &Tm1);
	strptime("2020-08-29 11:05:16", "%Y-%m-%d %H:%M:%S", &Tm2);

	if (mktime(&Tm1) >= mktime(&Tm2))		//Larger values of mktime() are more recent in time
	{
		printf("Tm1 is more recent than Tm2\n");
	}
	else
	{
		printf("Tm1 is older than Tm2\n");
	}

or with strptime() check

	struct tm Tm1 = {0};
	struct tm Tm2 = {0};

	if (strptime("2020-08-29 11:05:13", "%Y-%m-%d %H:%M:%S", &Tm1) == NULL)
		printf("strptime Failed\n");

	if (strptime("2020-08-29 11:05:16", "%Y-%m-%d %H:%M:%S", &Tm2) == NULL)
		printf("strptime Failed\n");

	if (mktime(&Tm1) >= mktime(&Tm2))		//Larger values of mktime() are more recent in time
	{
		printf("Tm1 is more recent than Tm2\n");
	}
	else
	{
		printf("Tm1 is older than Tm2\n");
	}

Get time difference in seconds

	double TimeDifferenceSeconds;

	TimeDifferenceSeconds = difftime(mktime(&Tm1), mktime(&Tm2));	//Value1 - Value2