Your first bill is normally produced within 10 days of joining the team and you can find out more details on the first bill here
In relation to changing the payment date, this can only be done after the 1st successful direct debit payment made.
The Refer a Friend credit wouldn't go against your account bill, this is a new process.
You will be eligible for the reward at the same time as your friend is. After you have had your services installed for 60 days, or if it’s a mobile order 60 days after the phone or SIM is delivered, you’ll both be eligible for a reward providing you've not cancelled the new contract within this time.
Once the cancellation period has expired, we’ll send your rewards to Virgin Media’s referral partner, Aklamio. In some cases, it can take up to five weeks after your services have been installed or their phone delivered for Aklamio to pop the reward in your referral accounts. Aklamio will contact you when the rewards have been confirmed, and both of you can have it paid into either your bank account or PayPal account at any time from your referral accounts.