If you hold the female outside the male's cage and watch to see what happens, they can't injure each other if the female is not receptive.
If the female rocks back and forth, hisses, gapes, darkens her body colors, lunges at the male, etc. then she is not receptive and you can put her back in her cage.
If the female is calm, moves slowly away from the male, keeps her peachy colors and the male acts towards her as if he recognizes that she's a receptive female, then you can put the female into the male's cage...but continue to watch them in case their reactions to each other change for the worse.
The female can remain in the male's cage until her background colors go dark or she shows other signs (hissing, rocking, etc.) of no longer being receptive.