Don't do it based on service hours, base it on when the blades are not sharp enough.
Hit a big batch of thick sticks the first time out of the box and you'll need to sharpen after 1 hour.
The right question is "How will I know when my blades need to be sharpened?"
The answer to that question is to look at your mower blades as well as the blades of grass after you cut them. Do you have big knicks in the mower blades? Do they look rounded? Are the blades balanced?
Then, look at the turf blades after you cut. Are they frayed? Is there a yellow hue to the lawn a few days after mowing due to that?
These can indicate that you need to touch up the edge and balance the blades.