After six months, infants need some extra food apart from mother's milk as infant's weight is doubled after six months and it is tripled when the baby's age is one year. Generally a child is born with some nutritious elements (for instance: iron) in its body. Those nutritious elements start decreasing once the infant cross six months. Therefore infants need nutritious food along with mother's milk after six months.
Babies are not introduced to certain foods earlier than six months may cause a higher incidence of food allergies. So try to introduce the baby with new food. If the food is tasty, the child will easily be attracted with the food and you need not to force him or her to have it.
There should be no certain time frame for the babies to have the food. The child will take huge time to eat the less amount of food in the beginning. So have patience and give your child less food. Keep in mind that the infant needs time to get habituated with the food.
When your child starts eating two or three table spoon food, you may try to include another new food. In this way, the child would be familiar with extra food and also be indulged with the food. Thereafter try to increase the amount of the food so that the baby starts getting used to solid food.
Keep in mind that the baby will not have same amount of food in every time. Observe your baby intensely when he or she takes food. If the baby doesn't want to have the food, he or she starts playing with the food rather than having it. It means the baby is not hungry at all.
Child will take time to have the new food and get used to it. So have patience and help your child to enjoy the food.