No, this is not common practice. Common practice is to space out EVLT treatments 2 to 3 weeks apart to minimize pain, bruising, and blood clot complications. It does not make sense to do the treatments 2 days in a row . . . .if you needed 2 treatments and the doctor wanted them done right away, why not do them on the same day?
The typical scenario is to either do all of the needed treatment on the same day or if it is felt that there is too much risk in treating both veins on the same day, then the treatments would typically need to be spaced out by at least a couple of weeks (it takes that long for the inflammation from the first treatment to resolve).
I would definitely talk with the facility about giving you a discount for the 2nd days treatment, as if they would have done them together on the same day, the cost of the 2nd treatment would have been dramatically less (the same equipment would have been used & it would have taken less time, dramatically decreasing your costs). When billing an insurance company for 2 treatments on the same day, the 2nd treatment is paid at a much lower rate for the above reason.