Sorcery and let it ride

Ok, say you want to disguise yourself using chameleon as a wizard or whatever that spell is called. For a normal disguise, the GM would say yes until a situation arose where the disguise would need to be rolled for. However, failed magic has complications pertinent to the time at which it is cast, eg failed spells can blow up.

Must you always roll when it is cast? Or can you let it ride?

A similar question applies to a rssearch roll that takes a month. Successes over the ob decrease the time it would take, therefore, shouldn’t the role be at the beginning?

Yes, you roll when you cast.

Yes you roll when you start researching.