Agree with the other guys, even a complete novice to car buying is going to ask about the timing belt even if they are unsure what it is, as it is what everyone asks for. You are going to lose out one way or another.
On the other side, buyers always expect to knock something off so leaving it allows them that discount.
Personally, I would do it knowing that you also have it done if you decide to keep the car or it takes an age to sell. I had my ED30 done early then sold it, cars like these have more appeal with proactive maintenance. I got a genuine kit, water pump and coolant for £324 fitted from an indy.