Its sort of a catch 22 in my experience. Its easier to call them from farther away in the early season, because there is no foliage on the trees and they can hear it. However, there are many more receptive hens in the spring, and since hens go to gobblers 9 out of 10 times, a hen will often find him before he finds you.

In the late season, when receptive hens get scarce and gobblers start grouping back up, you can really pull them from a long ways off, but, they can't hear quite as far as they could before.

No matter what the season I find that gobblers are typically easier to call in mid-morning, while they don't gobbler quite as much, they travel more. Often birds in my part of the world will gobble on the roost until a hen walks in to them, or fly down into a field and wait for them there. Some of them won't come to a hen PERIOD! Just depends on your local turkeys.