Question: Is it possible to grow tomatoes as a pot plant? In the limited space I have I can afford pot of maximum depth = 12 cm and diameter = 12 cm. what size pot will be ideal to start with?

In India what would be the best time to plant them and how can I take care of it at later stages?

Sun is not that harsh is winters here - temperature ranges 5-35 degree centigrade, average day temperature would about 24 degree centigrade.

Plant will be placed outdoors and will get all sunlight all through the day.

Answer: 
One of my best tomato seasons was when I was living in an apartment with a balcony that got sun about 4 hours a day. I grew 6 plants: 3 in each of two 18" pots. They were some variety of "patio tomatoes". That was in 1989. I didn't match the dozen dozen tomatoes I got that year until last year in my 4'X4' planting bed. However, this year a had one cucumber plant that yielded 100 cucumbers.
As an anecdotical answer, here's what happened to a slightly smaller undrained pot Φ~=80mm, h~=90mm. I had intended to transfer it to a larger proper pot but that never happened. The red thing is a 0.5 liter beer can for scale. The height of the plant is H~=500mm and the diameter of the fruit is d~=9mm. It is turning yellow now so I expect it to at very best double in diameter before ripening.

[![enter image description here](https://i.stack.imgur.com/rv7Cd.jpg)](https://i.stack.imgur.com/rv7Cd.jpg)