Historically in UK and Ireland services such as water, gas, electricity, phone were nationalised. Which is to say government-owned and run - not by private companies. When I was a kid playing Monopoly I used to wonder what "utilities" meant because we just did not have them.

For whatever reason the government chose a 90-day (quarterly) billing period and that is still by default in use today even though the utilities were privatised long ago. I am not a customer but I think you can switch to 30-day billing if you want to.

tl;dr that 73 day period is "normal."