Usually you can switch to 2 times a day at 6 months. Cut out the lunch.
My girls eat more in the morning, I guess because they've been sleeping all night.
How much you feed them is going to depend on your dog. When they are still under a year, you want to give them all they want because they are still growing.
By the time they are a year old you should be able to tell how much your dog needs.
Right now I am still free feeding my girls (they have food available to them all the time) because Koke is not a year old yet. When she gets to 1 year, then I will decide whether or not I'm going to continue free feeding.
But you have to understand that they don't always eat the same amounts everyday. Some days they are hungrier than others, depending on what they have been doing, how many treats they have had, if they have had a greenie or other edible chew, etc.