i have a feeling you were using a hammer to try to kill a fly
NOW() includes a time potion
so, for example, NOW() + INTERVAL 24 HOUR is actually 2008-05-30 14:09:37
however, your stored dates would be like 2008-05-29
at some point in the day, it only makes sense that an event would stop showing
it all depends on how you write your WHERE clause
NOW() is mysql's synonym for the standard sql CURRENT_TIMESTAMP function, and includes both a date and a time
perhaps you should be using CURRENT_DATE in your comparisons?