My question is why are you doing a two step starter? Is it because you don't have room for the volume you need? for what it's worth you can probably get away with a one step 2L starter, 3 liters would be better. If you only have room for 1 liter can you do more than just the two? If I need a bigger starter than I have room for in any one container I split the pitch into two smaller containers.
Because the yeast will hit maximum cell density at around 200 billion cells in a 1 liter starter if you pitch two you'll be pretty close to your target rate of ~400 billion. Whereas if you pitch the results of a 1 liter starter ~200 billion (likely a bit less) into another 1 liter starter you will have ~200 billion older, tireder cells.
One step starter for a 10 gallon batch of Helles? I'd be doing a 2 step for a 5 gallon batch.
Ferment the first step for 3-4 days, crash over night, decant and add new cooled wort. Step up from a 2 to a 3. I'd still think that's not enough for 10 gallons, but it might be...