I am evicting my tenants. I have started the termination process. They won't be out till November. I think the power company is turning there power off. How long can they live there without power?

As long as they can stand it. As long as the electric is in THEIR name and you are not shutting off the power (which would probably be illegal), they can stay as long as they can stand it.

Beware of what happened to me - tenants planned to leave without telling me, and didn't pay their electric for months, timing their departure for when it was turned off (and stiffing me out of some rent). The electric company wanted ME to pay their arrears! I had to fight and do quite a bit of angry arguing to convince them that I didn't know, how could I know, even living upstairs (and wasn't in collusion either). They finally relented.

Something they probably had to do by law anyway. But I needed the power on to that apartment that day and wasn't going to mess around with hard to research laws.

Also, location could be an issue. The electricity may be needed to keep pipes from freezing or other damage to the property.

Many jurisdictions require rental units to have fully functional smoke detectors. Most detectors (wired or all battery) have a backup battery. Are the tenant's smoke detectors operational or have they removed the battery to avoid the warning chirps? I would be concerned about the fire hazard and my liability regarding smoke detectors, not to mention all the other problems they can cause such as use of kerosene heaters, possible use of candles etc. Very undesirable situation in my humble opinion.