Most manufacturers recommend every 100k miles, however, I don't think your 1.8L is an "interference" engine; that is, if the timing belt breaks, the valves won't crash into the pistons upon belt breakage. So if you decide to push it, and the belt breaks, you won't be out the price of an entire engine!
Personally, I would change the timing belt at the recommended interval regardless of interference or non-interference; as the belt ages and stretches, you will gradually lose power and fuel economy. An engine with a fresh timing belt will typically run like a scalded dog. Timing belt changes are also perfect opportunities to change out idler pulleys which have bearings prone to long term failure, and water pumps (you have to pull the timing belt to change the water pump.. might as well when you're in there rooting around with a stick).
