Normally, when I wake up I don't have any hunger. I eat directly at 12:30 sharp due to work hours so I can go to the gym in afternoon? My question is: how much time should I wait for before I work-out?
First and foremost, you are following an extremely unhealthy approach. You need to have breakfast or eat within an hour of waking up. This will kick-start your metabolism for the day. Google skipping breakfast to understand what I mean.
As far as your question is concerned, it really depends on what and how much you eat for lunch. Ideally you can hit the gym floor about 45-60 mins after meal.
-- Update -- Breakfast most important meal