I don't think that's right. Their website says this:

    For your convenience, all Storm on Demand services are 
    billed hourly. This flexibility allows you to create and 
    destroy Storm Servers as you need them, and only pay for 
    the time you need.

https://www.stormondemand.com/servers/whystorm.html

It would appear you can bring up a server for 3 hours, and just pay for that.