LinuxQuestions.org - How do i change the time intervalls?

Hello guys! My webmaster is taking for ever i need to change some bugs and i hope you guys can help me out!

iv changed some of it but iv got almost zero experience of programming.. :/

The thing is this website is for my fathers company.
Hes out doing some real estate jobs and it takes about 3 hours
but the script only says no when ppl book at the exact same time.
so if you booked 08 AM and someone else tried also to book at the same date
and 08 AM it would say no.. but if you booked 0830 AM it would say yes :/
and that doesnt work at all since my father isnt aviable for like 3 hours and some driving time excluded...
How do i fix this? i need some exact syntax help here im really new

Sry for my english as im not a native speaker just let me know what you cant figure out and il try to explain

thanks!

PHP Code:




  switch ($_GET['steg']) { 
    case 1: 
        sysCalendar(!isset($_GET['datum']) ? date("Y") : substr($_GET['datum'],0,4),!isset($_GET['datum']) ? date("m") : substr($_GET['datum'],5,2)); 
        break; 
 
    case 2: 
        if (!isset($_POST['dDatum']) || $_POST['dTid'] == "") 
        { 
            sysError('Felaktigt datum/tid, var god ange både datum och tid.<br><br><a href="javascript:history.back(1);">Tillbaka</a>'); 
            break; 
        } 
        if (sysCheckDb(str_replace('.','-',$_POST['dDatum']).' '.substr($_POST['dTid'],0,2).':'.substr($_POST['dTid'],2).':00') == 'FALSE') 
        { 
            echo 'Tiden du valde är redan bokad/upptagen. Var god prova en annan tid som passar dig.<br><br><a href="javascript:history.back(1);">Tillbaka</a>'; 
        } 
        else 
        { 
            sysForm($_GET['tjanst']); 
        } 
        break; 
 
    case 3: 
        sysConfirm($_GET['tjanst']); 
        break; 
 
    case 4: 
        sysComplete(); 
        break; 
 
    default: 
        break; 
}