Egg laying is the pivotal event. When they get to that age, at around 6 months, you will want to shift them to layer feed. What you do prior to that makes little difference, as long as you are feeding 18-20% protein or more.
I keep it simple and use grower until they get to 5 months or so, then switch them to layer. I don't have a hard and fast timetable I stick to, I just do it when they are ready. You'll know when they arent babies and are ready to start on the layer.
Use common sense. Cocks fall in line with the layers and get the same feed.
AS for the feeding of grain, you should be careful. Grain should be only a part of their overall diet, as it alone doesn't offer enough of the right nutrients. In the wild, jungle fowl eat seeds, grains, shoots, nuts, grasses, insects, grubs, fruit, etc. They are really omnivorous eaters. Ideally, the "yard bird" would get a variety of grains, meat and green feeds, each in separate feeders and they could eat as they wanted of each.
This is impractical, so it is generally best to feed a prepared ration, some grain in the form of scratch or cracked grain as available and allow them to forage at will among green plants. The latter can be fed as supplement, if true range forage isn't available.