When you rent a movie via the iTunes Store, you have 24 hours from the time you start watching the movie until it is erased from your drive. That's marginally better than the situation with Comcast (my cable provider). With Comcast, the 24 hour clock starts ticking from the moment I rent a movie, whether I start watching it immediately or not—making me feel a bit like Jack Bauer in 24. With the iTunes Store, you have a generous 30 days within which to start watching the movie.

The problem for me, even with iTunes Store rentals, is that I often want to watch a movie over two nights. The 24 hour limit gets in the way here. If I start watching at about the same time each night, I won't get to see the second half of the movie—because I will have exceeded the time limit. A 36 (or even a 30) hour rental would make so much more sense. I know I am not alone here. A recent column by David Pogue makes the same point.

This is one reason I never rent movies from Comcast. It's also a reason why I have been reluctant to try rented movies from the iTunes Store. Still, I downloaded one the other day, primarily as research for an article I was writing.

With the movie now on my drive, I naturally began to wonder exactly how strictly the 24 hour limit was enforced.

It turns out that it's not enforced all that much.

What did I do? The most obvious thing I could think of. I changed the time. More specifically, after starting to watch the movie and putting the 24 hour countdown in motion, I went to the Date & Time System Preferences pane. From here, I unchecked the option to set the time automatically. Then I pushed the clock back a day.

Sure enough, iTunes now said that the movie had an extra day remaining before it expired. I still wasn't sure that this would have the desired effect. But it did. The 24 hour period passed and the movie continued to play.

With success coming this easy, I figured I couldn't be the first person to have come up with the idea. I was right. When I did a Google search, I found several similar reports.

There are couple of hiccups that can occur if you start pushing times around. iTunes may get a sense that something is a bit off. Occasionally, especially after changing the display size via iTunes' View menu, the movie window may go gray or the sound may stop playing. Often, just closing and reopening the movie a couple of times will get things working again. As a last resort, I found that if I quit iTunes and reset the clock to less than 4 hours from the expiration time, the movie would always work fine when I relaunched iTunes.

I've made no attempt to see whether the extended time limit would hold if I transferred a movie to an iPod or an iPhone. I see possible complications here, as these devices have their own clocks. But I leave that for someone else to worry about.

In any case, I imagine that Apple will eventually find a way to prevent these time extensions from working. But who knows? Apple at first tried to block iPhone users from creating their own ringtones for free. In a 180 degree turn-around, Apple later not only ended the blockade but offered tools for creating ringtones using GarageBand.