When is the function delay() a delay?

Well, in theory, delay(2000) should delay for 2 seconds. As per https://www.arduino.cc/reference/en/language/functions/time/delay/

However, there are some potential caveats - for example:

What board are you using? (ESP8266's for example, don't like to be kept waiting and will crash out by watchdog timer)
Are you using the right "core" settings in Arduino for the board? (if the clock crystal on the board is not matching the expected clock rate, delays could be wrong.)
Are you doing something else with the timer peripherals on the microcontroller that could interfere with the Arduino code?

Try this - what does a simple LED blinky sketch with delay do? Does it wait the expected amount of time? Or alternatively code your delay by checking millis() - does that work or not?

- Gough

I would start by putting a serial.println before and after the delay just to make sure there’s no question of it being the right delay line you’re looking at.

 Also make sure you have selected the correct board for your sketch. There’s a good chance delay() just counts clock cycles, so a faster chip might whip through them faster than a standard old Uno might.

Im a sw fumbler myself, Ill throw out a couple suggestions. variable relayDelay() wont be recognized as a Arduino delay command. The other delay(300000) should be too big a value, even tho it works. The delay value is an integer, 32767 max (or maybe 65535 if unsigned). There are some online articles that talk about some Arduino commands that interfere with the delay timer time accumulator in background. 

The standard Arduino library defines the millisecond value as a (32-bit) unsigned long. So you can use values considerably larger than 32767/65535.

The issue people tend to run into is when they multiply two integers. For example, delay(3000 * 1000); Since both values fit inside of a 16-bit data value, the complier treats the operation entirely as 16-bit even though the result overflows. All of that happens despite the (correctly) result fitting inside of a 32-bit value which would work if explicitly written. (or if the math is casted.)

This. Maybe use a digital output. Flip polarity before the delay. Flip polarity after delay. Use an oscilloscope to measure the time.

The board is a Geekcret Arduino Mega 2560 (on chip) knock-off.

I'm not manipulating any timers.

The program reads a set of eight IR sensors divided across two tracks. Four sensors on one track four sensors on the second track. The four sensors per track are divided down into pairs. One pair is departure and the other pair is arrival. The exercise is to read a model train motion as it passes over the sensors. A sensor reads 0, when the train is over it. The sequence: stop (0000), departure(0011), in transit(1111), arrival (1100) and stop (0000) as the train moves from right to left over the sensors.

I tried the exercise of confirming the timing of delay. If saying one-steamboat is a second (old touch football trick) the Blink sketch from examples flashes on & off for the number of seconds set up in delay().

I didn't explain myself well

relayDelay() is  void function i created

void relayDelay() {
  time_now = millis();
  while (millis() < time_now + turnout_delay) {
    //wait approx. [period] ms
  }
}

that I could use to test what amount of delay I would need in order to activate a relay so the contacts make. Currently turnout_delay = 10000 and I get about 1 second the relay is engaged. Now this throws a wrench in my understanding of delay() but the time duration works.

Any reference links on Arduino commands that impact delay timer?

That was my low tech way to confirm the code was actually running.

I drop these lines of code in to use serial print

    if (deBug == HIGH) {  //tell status
      Serial.println("Mark");
    }

By setting deBug variable I can make the serail print disappear to reduce any impact to the code operation when in production.

The delay() is not the three seconds I hoped for when I bookend it with the serial print lines.

What is the type of time_now variable? What is the type of turnout_delay? Are you sure you have enough free RAM?

If you're not using unsigned long, then you are probably running into overflow issues as millis() reports unsigned long and if working as other data type, will not handle roll-over correctly.

- Gough

Good. This means your board set-up is fine and the problem is most likely in your code ... check data types as I had noted in my other reply.

- Gough