It's up to you where and when you want to ride.
Just remember that in Free Login zones you can always go online and ride with Deliveroo whenever you want, without booking your sessions in advance, all you need to do is open the app when you are inside the login area, go online and start accepting orders.

For all the other zones, you will book your sessions through the Deliveroo Rider app.
So you will book your sessions each Monday at 3pm for the following week and all the next days if you find sessions still available.