Emily has insomnia and some behavioral side effects (agitation, primarily) with Prednisone, but usually not until she's been on it for several days. She does, however, start gaining relief quite quickly- usually within the first 24hrs. Three days, as posted above, is probably short enough dose to spare you major side effects... except the potential for your cfrd being affected, which I imagine could be affected much sooner. I hope you do ok with that- it's good you are ok thus far! I'd recommend checking your sugar more often than usual to be on the safe side, since even people who don't have cfrd can sometimes have trouble when on prednisone.
She has generally needed a much longer course when she is sick with bronchitis; after unsuccessfully trying a shorter course she's needed 10 days or so; the first 5 days at 10mg bid then a taper for 5 days.