The cyanotype takes 24 hours for the oxidization to bring up the full image density.
To create instant oxidisation (changes to a brilliant blue) place in a water bath of 0.3% hydrogen peroxide for no more than 30 seconds
Continue to wash as usual.
Interesting fact – Hydrogen peroxide was discovered in 1818 by the French chemist Louis Jacques Thenard. Thenard called his creation “oxygenated water” because it is essentially water with an extra oxygen atom.