gaining accurate time on time sensitive measurements.

Projects General Guidance
12

removing the floats could look like:

#include <Adafruit_CC3000.h>
#include <Adafruit_GPS.h>
#include <SD.h>
#include <SPI.h>
#include <string.h>
#include <SoftwareSerial.h>

#define WLAN_SSID      "myNetwork"
#define WLAN_PASS      "myPassword"
#define WLAN_SECURITY  WLAN_SEC_WPA2
// Security can be the following; 
// WLAN_SEC_UNSEC, WLAN_SEC_WEP, WLAN_SEC_WPA, WLAN_SEC_WPA2

unsigned long lastTime = 0;
const unsigned long interval = 20;

long Vin;  // <<<<<<<<<<< made global

void setup()
{
  Serial.begin(9600);
  delay(2000);
  Serial.println("Hello World");
  delay(1000);
  Serial.print("Initializing SD Card.  Please Wait...");

  pinMode(10, OUTPUT);

  if (!SD.begin()) 
  {
    Serial.println("Card Failed, or not present...");

    while(1);  // blocks the script. return continues with loop!
  }
  Serial.println("Card was found"); 

  int ref = analogRead(14);
  Vin = 1125300 / ref ;             // Vin in millisVolts !  (iso floating points)  calculate only once..
}

void loop()
{
  unsigned long time = millis();

  if (time - lastTime >= interval) // by comparing you will never miss a read and subtraction is far faster than % operation
  {
    lastTime = time; // remember
    
    long sensorU = (Vin * 12 * analogRead(0))/1023000 - 30;
    long sensorV = (Vin * 12 * analogRead(1))/1023000 - 30;
    long sensorW = (Vin * 12 * analogRead(2))/1023000 - 30;
    long sensorQ = Vin * analogRead(3)* 500000;

    File dataFile = SD.open("datalog.txt", FILE_WRITE);
    if (dataFile) 
    {
      dataFile.print(time);
      dataFile.print(",");
      dataFile.print(sensorU);
      dataFile.print(",");
      dataFile.print(sensorV);
      dataFile.print(",");
      dataFile.print(sensorW);
      dataFile.print(",");
      dataFile.println(sensorQ);
      
      dataFile.close();
    }
  }
}

// code not tested, might contain some errors but you should get the idea