strtotime function expects to be given a string containing an English date format and will try to parse that format into a Unix timestamp (the number of seconds since January 1 1970 00:00:00 UTC)

Let's write the current date in the Unix timestamp format:

echo strtotime("now");

This is how you can add three days to the current time

echo strtotime("+3 day")

Converting the Unix timestamp to the current date and time

echo date("m/d/Y h:i:s",strtotime("now"))