You should submit your opening meter readings between 5 days prior to 5 days after your switch completing. So around 2 weeks after you sign up to Green.
Don’t worry though we will email a reminder to you, you can also track this in our App.
We will then send these readings to your old supplier so they can give you a final bill.
If you don't submit a meter reading, we will have to agree an estimate with your old supplier, this is less accurate than an actual read and may delay your final bill from your old supplier.