First, you can simplify your line like this:
$timeStamp = time() + 300;
This avoids a lot of internal operations and gives the same result. time returns the value in seconds, then just add 5 * 60 segundos, that gives 300, so PHP doesn’t need to make an unnecessary call to strtotime and a complex interpretation of strings.
Once done, just test if the result has dropped over the weekend, and add a day or two as the result:
$timeStamp = time() + 300;
$weekday = date( 'N', $timeStamp );
if( $weekday > 5 ) $timeStamp += ( 8 - $weekday ) * 86400;
- $weekday = date( 'N', $timestamp)obtains the day of the week, being- 1second and- 7sunday
 
- if the result is greater than - 5(i.e., Saturday or Sunday ), adds 86400 seconds (i.e., a day,- 24 * 60 * 60) multiplied by- 8 - $weekday, that gives a day if it is- 7(Sunday), or two days if it is- 6Saturday, effectively playing the schedule of the second.
 
Here we have a version with strtotime, more like your:
$timeStamp = strtotime( '+5 minutes', time() );
if( date( 'N', $timeStamp ) > 5 ) $timeStamp = strtotime( 'next monday', $timeStamp );
Or, keeping the time:
if( date( 'N', $timeStamp ) > 5 )
   $timeStamp = strtotime( 'next monday '.date('H:i:s', $timeStamp), time() )
But do not be fooled, although shorter this second version, it performs internally a much larger amount of operations far more complex than the first code, to make the textual interpretation of values. In short, it is technically inferior.
							
							
						 
http://www.timestampgenerator.com/ This site calculates the Stamp team
– Vinny Marques