SR4 Street magic says "If the spirit is asked to use a single power, it will continue to do so for as long as it is able to or until the conjurer asks it to cease." Is there a time limit on this type of service for a bound spirit? I can not find such a reference in the books. So a character Invokes a great form guardian spirit and orders the spirit to "Endow me with your elemental attack power until I ask you to stop." How long does that service last? Until the character dies if she never asks the spirit to stop?

iirc, there is a suggestion (possibly not in the books, might have been made here on dumpshock by one of the devs or freelancers or some random person) that you should count it as 1 service every sunrise/sunset.

Until the spirit is disrupted or banished, until the summoner is killed, or until the magician orders another service.

I think it's in the FAQ where it suggests that 1 sunrise/sunset counts as 1 service. So up to 12 hours (longer near the poles).

Isn't that what long-term binding is used for?