将天，小时和分钟转换为总分钟

Sorry if this is not the correct place to post this but doing research on Google I haven't been able to find a suitable answer.

What I want to achieve is a user types in a date and time on the site and this gets inserted into the database (two different fields, a date field and a time field).

I then need to get the total of minutes until that day/time. I have the following code which prints out the days, hours and minutes. But I'm unsure of how to convert it to a total of minutes:

date_default_timezone_set("Europe/London");
$now = new DateTime();
$future_date = new DateTime(''.$Date.''.$Time.'');

$interval = $future_date->diff($now);

echo $interval->format("%a days, %h hours & %i minutes");

$now = new DateTime();
$future_date = new DateTime($Date.' '.$Time);

$minutes = ($future_date->getTimestamp() - $now->getTimestamp())/60;

Unix timestamp stores the date in seconds. So you can calculate it without initialize a DateInterval with the diff() function.