Can someone help me review this schematic? (AT89C52)

I am a beginner and I have got few questions with the first project I am attempting. I am trying to build a reliable timer circuit with three timing options. The use case is very similar to a microwave oven i.e., the circuit should check if the doors are closed, three timing options that can be selected with the buttons, start, stop and pause options for the timer.

I first thought of using a 556 timer(restricting to only two timing options) with a relay. But I also needed a display(lcd...

Can someone help me review this schematic? (AT89C52)