The batteries are 8 amp hour batteries. However, the 8 amp hours means how much electricity they have to give, not how long they will last.
Like an 8 ounce glass of water, 8 ounces is how much water is in the glass. If the water is just sipped, the water in the glass might last for many hours. However, if the person drinking is really thirsty, the water might last only minutes, or less.
Your fire alarm system probably sips the electricity so the batteries should last about 24 hours, but don't count on it.
Keep in mind if it doesn't work, the panel doesn't cause a fire. It's just that if the primary AC power and the backup batteries quit, the panel is essentially dead and won't detect a fire. In other words, if there is a fire, no one will know about it until the fire is quite large.
Horns and Strobes
The horns and strobes only use electricity when there's a fire, so they should be left wired into the system.
When the panel quits working, that's when you need to use people to replace the panel's fire detection function. Someone or several people will have to walk through the whole place every half hour looking for possible fire.
Check with the fire marshal in your area about how the fire walks are supposed to be implemented, and to indicate what documentation is needed to show that the fire walks were performed.
Fix the Breaker
Fixing the breaker is the easy way to get the fire alarm system back to normal. It really is recommended that you get the failed breaker fixed right away, no waiting for estimates.