Fire attack is a 24 hour operation, day and night. Aircraft typically won’t fly at night but the fire activity usually slows at night as temps go down and relative humidity go up. A lot of back burns and firing operations happen at night when the weather holds the fire in check some more.

Honest question: why not fight it at night? Would be cooler with the sun down, and the target glows in the dark to the naked eye. No light no problem? I'm sure it's more complex than that