My question about prepaid roaming billing was closed. Perhaps it was too carrier-specific.
I've now edited it to make it non-carrier-specific.
Is it ready to be reopened? If not, is there some way I could improve it and make it ready?
I do not think you can edit this question such that it fits the site.
The answer will depend on the technical abilities of several networks, their policies on how to charge and their contact with your provider.
In some cases it may even depend on a single cell in a network.
As such it is too broad.
I have not voted when the question came up for re-opening but agreed with the vote not to re-open.
My working assumption has always been that billing is effectively immediate, more or less. There are many ways that the networks might achieve this, and the technicalities are beyond the scope of a travel site.
It has to be this way because any systematic delay in billing will quickly be discovered and exploited, losing revenue to the networks. Any delays that do exist will likely be dependent on the specific carriers involved.
Note that tracking network charges in real time is not the same as processing those charges for billing purposes.