I have been sent a 10 day window to submit my first readings on switch to Bulb. Will I get an actual date or is there a better or worse day in those 10 days to do it?
I’d guess that if you give readings on the switch date itself then these can be used to close your account with your old supplier and start your Bulb account, without the need for estimates. Unless they do something more exact, I don’t know.
It may be the case that supplying readings at the earliest opportunity will close and settle your old account quicker.
Somebody from Bulb should be able to tell you if there’s nothing in the Help pages.
[edited to add: you choose the date otherwise estimates will be used]