ESP8266 ISO 8601 string to tm struct
Try strptime from the time.h.
void setup()
{
    
  struct tm tm = {0};
  char buf[100];
  
  // Convert to tm struct
  strptime(&quot;2001-11-12 18:31:01&quot;, &quot;%Y-%m-%d %H:%M:%S&quot;, &amp;tm);
  
  // Can convert to any other format
  strftime(buf, sizeof(buf), &quot;%d %b %Y %H:%M&quot;, &amp;tm);
  Serial.printf(&quot;%s&quot;, buf);
}

void loop()
{
    yield();
}