There are really two things here: a "timed_output" class, and a "timed_gpio" driver that creates a "timed_output" device that drives a GPIO.
The "timed_output" class provides a single device attribute: "enable". It leaves the interpretation of that value to the driver.
Writing "0" de-asserts the gpio. Writing a number of milliseconds causes the gpio to be asserted for that long, then de-asserted.
Reading returns the remaining time before the output will be deasserted.
There are two things that timed_gpio provides that leds-gpio currently doesn't.
1/ high precision. leds-gpio uses jiffies-based timers so probably only to the nearest 4msecs. timed_gpio uses hrtimers, so give 1msec precision.
2/ read back of time remaining.
The only references to timed_gpio I can find on the web are for using it for the vibrator just like the above article says. I doubt that needs millisecond precision. If it did, a leds-hrgpio driver could be written (or an extension to the current driver) rather than a new class.
If the time-remaining was really important, then a 'one-shot' led-trigger could be written (rather than a whole new class) which reported the time remaining. That might be useful for other leds as well.