In pretty much all traditional and fully Torah observant Jewish homes, you're bound to find "24 Hour" Candles, which are needed on certain holidays and when observing
Yartzeits, anniversaries of deaths. When I was growing up these 24 hour candles were in glasses, which were always washed out well after the candle burnt out. And those became our drinking glasses. Nowadays, at least in Israel, the 24 hour candles are in metal cups.
For a number of years already, many people I know have been noticing that instead of the 25 hours or more they used to stay lit and be needed, nowadays, they don't last even twenty-four 24 hours.
To be honest, twenty-four 24 hours are not enough for some purposes. They really need to stay lit for twenty-five 25 hours. That's because if you have it lit on Rosh Hashanah in order to light the second night, that's twenty-five 25 hours after being lit. If there's no light/fire, one can't light the Holy Day candles. In my neighborhood, we've all come to each other's house in a panic looking for a light/fire to light from. And then we have to very carefully go from house to house with the lit candle to be used to light another. Sometimes, because we were too young to think of having
Yartzeit candles in our homes, and the logistics of getting everything ready we'd forget, but more often, we lit, but the candle didn't stay lit long enough.
The candle needs to be still going strong after twenty-five hours for Yom Kippur, too, since it's traditional to light the
Havdalah candle from a burning flame, lit before the fast/holiday.

For years already, I've been using candles that say 48 or 72 hours because of this problem. Before the Yom Kippur fast began, just seconds before lighting the holiday candles, like for Shabbat, I lit two different
Yartzeit candles. One was one of those 24 hour ones, and the other a 48 (actually 50 according to the label) hour one. I'm sure you're not surprised that only one of them was still lit when we came home from shul. And in case you don't know, our shul is just behind the house, so we didn't need to travel or take a long walk.
A neighbor had asked to come for Havdala, since her candle had gone out pretty early. She said that many others had complained to the company and never received replies. So after we ate, I decided to blog about the issue and the suggesting that people do what I do and get longer-lasting candles. To do this I took some photos of the candles. And what do you think I discovered?
Not only don't the candle manufacturers attempt to give you enough wax for the needed 25 hours, which was once the norm, they now protect themselves by writing on the can in Hebrew and English:
"Burns About 24 Hours"
Next time you're buying, check to see what it is. They sure don't make 'em like they used to...