Frankie tied with Squish on June 27th. Her first litter was delivered on day 58 (counting from the tie)

That gives us a delivery date of/about August 24th. 

Sperm stays viable for two+ days, so it's possible to have 2+ days play on the delivery. The fastest sperm create females and the slower create male pups. 

In this first 1-2 weeks fertilization occurs and the eggs implant. The eggs leave the fallopian tube and head for the womb. Each baby develops in its own sac and they are linked like sausages.  There are typically 2 "horns". The babies closest to the nutrition grow bigger and further away, smaller. 

It seems when they are delivering the sizes are biggest to smallest (one side) then I (they) have a bigger baby, with the next delivered getting smaller again.

The number from the first side gives me an estimate for the second 

The babies are busy dividing cells (remember biology class?) And grow from a single cell to 64. 

I don't do xrays or ultrasounds. Primarily those are done for the purpose of knowing how many babies are coming. While the counts are correct most of the time, they are also off a lot. Momma's know what they are doing. If we give them time and support they deliver and recover. I make plans with the "I have babies due that weekend" clause. I sleep in the room with Momma once pre labor has started. The girls are very comfortable with me and my touch. I take temperatures twice a day leading up to delivery. I have cams on the Momma if I have to go out. 

1 week for a dog = 1 month for a human. At this stage there are no restrictions on exercise or food. Frankie produced above average size babies the first litter, her human keeps her healthy and on a quality diet.  She delivered a litter of 5 naturally.