Test if time is between two times

I have an action that sets current time in the DB.

I want to run a cronjob on a 5min interval to check for documents that is not set 5min ahead of time when cron runs, but also not in the past of when the cron runs and then perform a certain action....

Id tried it with the following code but its not working... Any ideas?

$t=date("H:i:s", time());
echo $t.'<br>';
$currentTime = strtotime($t);
$futureTime = $currentTime+(60*5);
$plus5min = date("H:i:s", $futureTime);
echo $plus5min;

$inbetween = $currentTime+(60*3);
$plus3min = date("H:i:s", $inbetween);
echo '<br><br>'.$plus3min;

if (($plus3min<=$plus5min) && ($plus3min>=$currentTime)){

echo '<br><br>inbetween';
}else{
echo '<br><br>Not Now';
}