Am I charged twice if I terminate a Genymotion instance and start a new one within the same hour?

No. The billing is hourly, so the charge depends on the total time the instance ran, not on how many times you started or stopped it within that hour. How will I be charged for Genymotion on Alibaba?

If the combined runtime is 1 to 60 minutes, it is billed as 1 hour. If it reaches 61 to 120 minutes, it is billed as 2 hours, and so on.