How do I get or set the position along the timeline using MEL?

You can set the current time with the currentTime command.

You can query the currentTime command to return the current time in a format controlled by the currentUnit command.

The following commands store the current time in seconds in the $time variable:

// Save the current time unit in a variable
string $timeFormat = `currentUnit -query -time`;
// Set the current time unit to seconds
currentUnit -time sec;
// Store the current time in $time
float $time = `currentTime -q`;
// Restore the original time unit we saved earlier
currentUnit -time $timeFormat;