When and how does the notion of creativity manifest itself for you in aikido?
Self defense is ultimately an improvisatory skill. This has to be emphasized from the beginning. Even so, any creative or improvisational discipline has certain formalisms which facilitate creativity. This is true in music, dance, visual arts, comedy, and it is true in budo. So form and freedom of expression go hand in hand, and must not be allowed to be in conflict.
Degrees of creativity should be present in any activity. Bursts of creativity tend to manifest where mistakes are made, when we are surprised or momentarily confounded. When we become accustomed to patterns, creativity tends to be latent, but this is a natural part of the process. When our habituated patterns no longer make sense, then new patterns can emerge or old patterns will coalesce into a richer field of possibility. Old patterns may stop making sense either from the tedium of repetition, or from sudden confrontation where the circumstances do not fit the expected pattern.
Randori and jyuwaza are supposed to provide environments for this stressing of patterns, but really, one can have an "aha!" moment from within the confines of the most rigorous kata just as easily.
Finally, I hope we can recognize that true creativity is happening with greater frequency among beginners than with advanced students. What beginners create may not appear to us as innovative or brilliant as what advanced students are capable of, but nevertheless, by the very nature of being a beginner, we are forced to find our own creative solutions to overwhelming information and stimulation.