This would be one of the examples that may server your purpose.
$timestamp=time(); //current timestamp
echo "Current Time: $timestamp<br>";
$tm=$timestamp+172800; // Will add 2 days to the $timestamp
$da=date("F j, Y, g:i a", $timestamp);
echo "Current time string: $da <br>";
$da1=date("F j, Y, g:i a", $tm);
echo "Modified time: $da1 <br>";
check this method, will this do?
$dtm=2; // This is the no of days to be added to the given timestamp $timestamp
$da = date("F j, Y, g:i a", $tm1);
echo "Date $da <br>"; //The added date
You can make little more changes to the code and can make it as you wish