The AceTimer version was an old LDB-1.0 test plugin that got "accidentally" converted to LDB-1.1. I think for such an easy task AceTimer is too much, so it uses OnUpdate now. It's just a simple function call every 1/60 seconds (seconds/minutes mode).
The true value of AceTimer comes when you have many timers. The reason why all my timers use AceTimer. It's a lot less stressful on the CPU than many OnUpdates. (Exluding places where you're updating multiple times per second)