Many airlines operate a policy which mirrors advice given within the "Yellow Book", the common name for "Health Information for Overseas Travel" first issued in 1995 by the Department of Health as a companion to the already popular "Immunisation against Infectious Disease" (aka "Green Book").
"It is advisable to wait 24 hours after a plaster cast is applied before a flight of under two hours and 48 hours if the flight is longer (or bivalve the plaster)."
This advice is, of course, not relevant in the case of a cast applied 12 days previously.