Haneda (HND) is about 15 km from central Tokyo - close enough that a taxi is a realistic option. Narita (NRT) is about 70 km out, in neighbouring Chiba Prefecture - a genuinely long way from the city centre.
From Haneda, a taxi typically takes 30-50 minutes, the train 20-30 minutes. From Narita, the fastest train (Narita Express) takes about 36-90 minutes depending on your exact origin and which service, and driving typically takes 70-110 minutes.
For an international midday departure, our model's typical door-to-gate time (airport-side only, not counting the trip in) is about 109 minutes at Haneda versus about 172 minutes at Narita - the airport itself is also larger and busier at Narita on top of the longer trip in.
These are general, statistically-modelled estimates - not a guarantee. Always allow extra time for anything unusual, and check your airline's and airport's own current guidance.