Repairing Disabled Gun

Recently, broke firing pin in Marvel during match and no backup gun available. I've heard rules allow 20 minutes for repair and continuing shooting. Is this 20 minutes provision an actual rule or just hearsay?  Or, alternatively, can/should/must match director allow a "make-up" during a another relay or afterward?

There is no "20 minute" rule.  Disabled pistols are covered under rules 9.5, 10.9 and 10.10.