Will it affect my 6mth old baby development when he sleeps in d baby carrier for 1-2 hr. Upright position. Will it be too straining on the neck?

No; should be ok. A baby is very flexible, so sleeping 1-2 hours in a baby carrier is no problem, if he is buckled in a good position. Babies who frequently go on long commutes or vacation trips will spend many hours riding in car seats. They don't seem to get neck problems from the car rides.
Strength. . I believe that this might be a good beneficial position for your baby on occasion to help build strength in his her neck muscles. .