questions about billing

questions about billing

I understand that there are 3 types of plan (per hour, per request or fixed), and this plan is attach to account using contract billing.
but I have lot of questions:

is this only for ticket closed? also open?
(if per hour plan). does it count the real open-close time or the worklog time? is there is no worklog added?
does it count the open or the close date to check if the ticket is considered?
when does the bill cycle start: year calendar or start date? (example halfyear)
what's going on with the current billing cycle if not complete yet but the expiry date is reached?
Thanks in advance

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