Hamlet: How can we argue that Hamlet's delay of killing the king was reasonable? Any suggestions?

Hamlet wanted his father's killer to be punished, not just on earth, but in the afterlife too. Hamlet had a chance to kill his uncle, but it was during his uncle's prayer session. Therefore Hamlet felt that the king would be absolved of his guilt in Heaven. He wanted to wait until his uncle committed another sin before he killed him.