// lets define the working files
define("FILE_API_TIMESTAMP", "api.timestamp.txt");
define("FILE_API_DATA", "api.data.json");
// initialize main vars
// last api call
$last_call = 0;
// latest api data
$api_data = false;
// this moment timestamp
$current_time = time();
// check last api call from saved file
if (file_exists(FILE_API_TIMESTAMP)) {
  $last_call = floatval( file_get_contents( FILE_API_TIMESTAMP ) );
}
// if more than 60 seconds passed since last call,
// call API then save results
if ($current_time - $last_call > 60) {
  // get new data
  // $api_data = getApiData(); -> put your function here: Curl etc...
  $api_data = "new data: ".time(); // just an example
  if ($api_data) {
    // if new data is available,
    // - log the current timestamp
    file_put_contents(FILE_API_TIMESTAMP, $current_time);
    // update $last_call for later use
    $last_call = $current_time;
    // - save the new data
    file_put_contents(FILE_API_DATA, $api_data);
  }
}
// check if we have new data, if not bring old data
if (!$api_data) {
  if (file_exists(FILE_API_DATA))
    $api_data = file_get_contents(FILE_API_DATA);
  else
    $api_data = "no_data";
}
// finally, give the user the updated data:
echo "Data updated at: ".date("d-m-Y H:i:s", $last_call);
echo "<hr/>";
echo $api_data;