Would he pay for the same service both in the case of early and late rain? Would he need the service for the same reason in both cases? Is it a financial service? Is agriculture relevant? Relevant how much rain did come at the right time? Relevant what weather it was when it did not rain? Could any other weather phenomenon at the wrong time have made him pay? Could any weather other than rain at the right time helped him with not having to pay? Did he expect the rainstorm to arrive when expected? Did he expect to have to pay? Relevant for how long the rainstorm lasted? Relevant how rain affects: soil? Waterways? Drains? People? Vehicles? Asphalt? Temperature? Animals? Plants? Umbrella sales? Rollercoaster queue times?
Edit: would he lose money if no rain was expected, but had come at the time it did anyway?