I suppose it depends on how you are storing your datefield.
Assuming your datefield is timestamp(14) you might use...
$sql = "SELECT * FROM [table] WHERE [timefield] >= now() +0";
That will give you up to the second results.
if you don't have the time in your timestamp you could use
$sql = "SELECT * FROM [table] WHERE [timefield] >= CURDATE() +0";
That way you can have up to the second results.
BTW...it's usually quicker if you let mysql do the work
oh yeah and this always helps
RTFM