Best answer by Transparent
However... for my first three months with OVO I was sending in meter readings 14 days early, on 1st of each month. This isn't a problem because OVO's in-house Billing System can still use these to calculate a fairly accurate Estimated Reading for the date they use when generating the Statement.
For obvious reasons, the Estimated reading may well have a very slight bias in favour of the reading being higher than it actually is. Thus a Customer doesn't get a shock the next month when the Bill suddenly adjusts for OVO having had two months of taking too little payment.
So the closer you take your reading to the advised date, the better.
Actually some people don't send in meter readings for months at a time. They obviously suffer somewhat from receiving Estimated Bills, but OVO's system can still cope!