I think that's a Saturday so if your not working suggest can afford to wander around happily for a few hours. My routine on LH tends to be get through security (thats the random factor in how long to allow!), dump the bags in left luggage in lounge, book in for a spa, grab something to eat, then have a wander around shopping centre (always remember your boarding pass/flight number) and back for a bit of sit down and time for a game of russian rollette on the when will I go to the gate!

Suggest you will fill 3 hours no problem.