I have civic 98 with same morning problem or after 10 hours approx. I change the 3 times fuel pumps, injectors, spark plug, filters etc but no change happens.
I contact with Honda representative, they advice me to change coolant temperature sensor but till now i didinot change because of time.
Yesterday, mechanic change the cables of CNG switch for direct start on CNG and now the car start in 1 or 2 selfs
Hope it will help u.