hi shipra pls read everything under @pregnancy must know - there are lots of helpful articles there. just go to search and type.

Post meal ,, times is up to you if u are doing household chores then once in a day is good with a light exercise( prescribed by ur doctor)

Post dinner walking is the best ..take small walks then ...take care

Walking 20-30mins at the most morning or evening is good. However if you are prone to gastric trouble dear you can take small meals, walk for ten minutes and repeat after every meal. Eat light and in intervals.