Shit, I don't have time to answer those in depth right now- I have to do a calibration on my fucking bitchy gas chromatograph which is pissing me off royally.
If you need to flush, don't wait.
If you can't repot right away, punch a BUNCH of extra holes in the cup for added oxygenation to the root zone and also to allow the soil to dry after the flush- even on the sides- make them about 1/4" diameter.
You can switch to 24/.0 anytime. No prob. Under 85'F is tolerable, but that's the upper limit of heat.