The way you have the code for the date is not valid. You will need to set a variable to the current date and time in the format you specified like this:
$the_current_time = date("Y-m-d G:i:s");
You would then insert this variable into your db. If you are not familiar with using variables in this way you can add in an extra hidden form element and set it's value the same as above with the date function. Then you can specify this posted element for the time in the db.