code:

// Button is pressed!  We need to make sure the pump stops running after 5 seconds and doesn't run again until the button is pressed.
// Get the current 'time' the button was pressed using millis().  Make sure to store it in a 32-bit unsigned type.
uint32_t buttonPress = millis();

// Now add 5 seconds to the button press time to know when the pump should never be running.
uint32_t pumpStop = buttonPress + 5000;  // Remember it's milliseconds, 1000ms = 1 second.

// Be cafeful, pumpStop might be LESS than buttonPress!  This happens when the millis() counter is
// within 5 seconds of overflowing.  We'll deal with this later in the loop below.

// Main loop to start the pump and check if the contacts are pressed to stop it.
while (true) {
  // Check if the contacts are pressed that tell you the pressure chamber is full.
  // When filled stop the pump and break out of the loop.  Consider yourself in a pump stopped state until the button is pressed again.

  // Check if we've exceeded the time-out/pump stop time.
  // First grab the current 'time'.
  uint32_t now = millis();
  // Now check if we expect millis() to overflow during the normal pump running time, i.e. pumpStop is less than buttonPress.
  if (pumpStop < buttonPress) {
    // Expect millis() to overflow, so check if the currentTime is greater than the stopTime and less than the startTime to know when to stop.
    if (now >= stopTime && now < startTime) {
      // We hit the pump stop time!  Force the pump to stop and break out of the loop.  Consider yourself in a pump stopped state until the button is pressed again.
    }
  }
  else {
    // Else millis() will not overflow during the normal pump running time, so just check if it's greater than the stop time.
    if (now >= stopTime) {
      // We hit the pump stop time!  Force the pump to stop and break out of the loop.  Consider yourself in a pump stopped state until the button is pressed again.
    }
  }
}