Hi,

Also if you are in HND before 5pm you could also try the Cathay pacific lounge ( it is very good also)

I agree with JALPak, you could go landside and explore the Haneda airport garden complex connected to T3 ( with an onsen as well as shops and restaurants) or go into the city.
( i did spend 7 hours in t3 last year and time passed fairly quickly, I started off at the cathay lounge before it closed at 5pm then tried the JAL skyview business lounge ( pretty good) before going to JAL F lounge). This was before the Centurion lounge opened. Also walked from one end of the terminal to the other end ( about 2km all in iirc )
On another long layover ( 6 hrs during the day albeit transferring to a domestic flight I had a quick walk through the Garden complex ( just before the shops opened at 10 am ) then took the express monorail to Hamamatsucho station and walked around the Kyu shibarikyu garden ( beautiful garden and it was a sunny day)
Regards

TBS