I've been doing Ludum Dare for 7 years now, and I've always had trouble managing my time. I always think I have enough time, until I don't. In recent years I developed a technique to improve my time estimations. Basically every hour I write down what I'm doing in a timetable like this:

What I like about this is that I can use my spatial intuition to compare time spent between programming, design, art, and sound. I can also look at the filled space and compare its size to the unfilled space to see how I'm doing overall. Also, the hourly update ritual keeps me accountable as I consider my priorities during the jam.

Hope that helps you with your next jam!

Oh, and you can check out the game I made this weekend, called Icy Mountain Hot Potato!