PHP switch: calculate dates - php

Question

I made this switch, but I dont know this last step (the ?? and the comments).
If someone can help me, thanks a lot!
<?
$nuDatumTijd = date("Y-m-d H:i:s");
$nuUur = date("H");
switch(true)
{
case $nuUur > 8 && $nuUur < 13:
$aantSecErbij = ??; // number of seconds untill the first next 13:00
$weerOp = date($nuDatumTijd,$aantSecErbij);
echo $weerOp;
break;
case $nuUur > 12 && $nuUur < 18:
$aantSecErbij = ??; // number of seconds untill the first next 19:00
$weerOp = date($nuDatumTijd,$aantSecErbij);
echo $weerOp;
break;
case $nuUur > 17 && $nuUur < 22:
$aantSecErbij = ??; // number of seconds untill the first next 9:00 (so that is the next day)
$weerOp = date($nuDatumTijd,$aantSecErbij);
echo $weerOp;
break;
}
?>

Answer 1

I now have fixed it this way, thanks for your input:
$nuUur = date("H");
if ($nuUur > 8 && $nuUur < 13)
{
$weerOp = strtotime('today 13:00');
$weerOpNetjes = date('Y-m-d H:i:s', $weerOp);
echo $weerOpNetjes;
}
elseif ($nuUur > 12 && $nuUur < 18)
{
$weerOp = strtotime('today 19:00');
$weerOpNetjes = date('H:i', $weerOp);
echo $weerOpNetjes;
}
elseif ($nuUur > 17 && $nuUur < 22)
{
$weerOp = strtotime('tomorrow 9:00');
$weerOpNetjes = date('H:i', $weerOp);
echo $weerOpNetjes;
}

Answer 2

switch-case can be used this way too, no problem about that.
$aantSecErbij = ??; // number of seconds untill the first next 13:00
If this means the number of seconds until today's 1pm then the following will get you the timestamp of today's 1pm.
$now = getdate();
$time1pm = mktime(13, 0, 0, $now['mon'], $now['mday'], $now['year']);
If it means the number of seconds between now and today's 1pm then you need to subtract with current timestamp.
$now = getdate();
$diff1pm = mktime(13, 0, 0, $now['mon'], $now['mday'], $now['year']) - time();
.
$aantSecErbij = ??; // number of seconds untill the first next 9:00 (so that is the next day)
For the next day you can add 1 to the day part and don't have to worry about the end of month. PHP will figure out the right date for you.
$now = getdate();
$tomorrow9am = mktime(9, 0, 0, $now['mon'], $now['mday'] + 1, $now['year']);