A 1 HP motor running for 24 hrs. will consume the same amount of energy as a 2 HP running for 12 hrs. Here is the calculation:
2 HP x 12 Hrs x .7457 Kw/ Hp-hr x .12 $/kw = 2.15 $/day
1 Hp x 24 x .7457 x .12 = $2.15
You mention 8-10 hrs per day vs. 24, the only savings will come due to the shorter time of operation, not due to energy consumption.
The real question is how effective are the two methods.
I hate it when people try to misle me!
Yes, that said, does his service provider charge for tiers and time of day? If you exceed a certain level, they bump the cost per kwh meaning overall cost of ownership might be lower with a pump that draws less. Of course, if they charge more at peak then a stronger pump that can turn the water over faster but runs off peak would be the better choice.