i recently have been having heat issues in my home, furnace died, cost a couple thousand to repair it. what temps are safe for the plant during flower stage when the lights are of? below what temp is bad?

In my opinion 55-65 are good night temps. Low 50s is pushing it and you don't want anything under 50. What temps are you running right now?

lights are off. its 55 now, the lights come on at 7pm and go off at 7am. i decided to run the lights at night,because the nights are still chilly. this way the cool down will not be to bad, cause the sun heats everything up. the high temp today was 40 outside

les than 58 in root zone is going to slow you down big time...
Not room temp but root zone temp...usually a bit higher than room temp...
my two cents..

I've dipped to low 50's a whole bunch during a flowering session, and even 48° one night. That harvest I pulled 26 Oz's out of a 4x4 tent with 1200 watts of light.

Not sure what that all means.. but just throwing that out there. I'm often 50°-55° during lights off in these winter months. I run two (large space that's why) electric heaters in the room, both on low to maintain standable temps. Interesting though, my tent went up to 95° the other day during lights on. It was a random warm day we had last week.

lol i too have been fighting this fluctuation in cold and warm days, its still not warm enough at night for me to stick my exhaust panel back in the window as the backdraft cools the room far too much, its been interesting but iv been able to maintain 80f steady during lights on and 74 at the lowest at night, hopefuly this warm weather keeps up im really looking forward to getting rid of this winter already its been too cold and snowy for too long lol.