The new rule is the timer starts when the player clicks the 'Click to Land' button on the planet information page.

Starting the timer the frame the player actually moves Lenny leads to timing manipulation that I feel would make the category worse, such as avoiding the Martian on Mars by waiting to move until the Martian can be avoided without stopping.

The timer still stops the frame Lenny's spaceship starts to open.

As a general tip, stopping your timer just after the ship opens makes verifying runs easier than trying to stop the timer frame perfectly and accidentally stopping it early.

I've removed my Mars run and will be making another attempt in the future using the new rule.