can I add a time sheet to a task

[Ian]

I want to be able to keep hours worked on a topic/checklist item for billing purposes and evaluation of work produced. Is this possible?

[Torben_trello]

While that feature's not natively supported within Trello, we've collected a list of different extensions and integrations which offer time tracking within Trello here: Time Tracking. 

[Ian]

Thanks, it seems however that the timer is driven by the time on the card, is this correct. If so it is not what I am looking for. I want to be able to arbitrarily lodge a time in for billing purposes which may not be the time spent with the card open.