So much depends on the type of pasture and amount of pasture you have.
Longhorns tend to require about 80% of nutrition that other breeds do to maintain condition since they convert food more efficiently. However, one can have a BCS of 3 or 4 on a Longhorn or a BCS of 5-6. Depends on quality of nutrition, genetics, one's objectives, and all.
Longhorns tend to mature slower than some of the other breeds. A 205 day weaning weight can range between about 300# and 600#: a lot depends again, on nutrition, genetics, stocking rates, etc.
Just remember that with Longhorns you are not raising "feedlot cattle". The Longhorns tend to have a ADG of 1.5 to 3.0 lbs, depending on all of the above comments. They tend to "mature" at around 3-4 years old (in terms of horn growth and other factors). However, the LH are easy calving, breed back quickly (with proper nutrition and mineral program), and are service age (bulls and heifers) at usually 14 months old.