On a 90 Accord, the interval is every 90K miles. Honda also recommends if you do not drive it much, that it should be replaced every 7 years. On this model, also replace the water pump and put a retainer on the oil pump shaft seal (seal likes to pop out). I know of many Accords with 300-400k on them and still running strong.
Unless you have x-ray vision, there is no way to tell. On Hondas in particular, it is very important to change the timing belt as recommended. Hondas use "interference type" engines, which means that the valves and pistons occupy the same space, just not at the same time. Result being, if the timing belt breaks, (especially at higher rpm's), you end up causing major top-end damage to your motor. Include 4 valves per cylinder, depending on the engine, (assuming you do not damage any of the pistons)and the repair costs can get really ugly. Better off to replace it before it ever breaks. An ounce of prevention is worth a pound of repair.
You are mistaken, the 1990 Honda Accord is an interference motor. Some newer models may not be, but you should follow the guidelines by Honda as to when to change it and not wait until it breaks and risk possibility of engine damage.