We send your telematics device by 1st Class Royal Mail, so it should arrive a couple of days after your policy starts.
You're covered from the moment your policy starts, so you don't need to wait for your device. Just make sure you get set up as soon as it arrives – and download and log in to the app in the meantime.
It's a condition of your insurance that you and any named drivers download and log in to the app on your phones as soon as possible.