The cast time is calculated when you start casting, and the buff duration/potency is calculated when you finish casting. So yes, you can swap to -SST/FC gear before you cast, and duration/potency gear in the middle.
that is hilarious, and ridiculous - and good to know.
So in other words it is totally worth macroing in the whole +2 set at the end of every song to get duration?
Man this job is a gear pig.
When it comes to sitting around not doing anything for long periods of time, only being active for short windows, and marginal changes and sidegrades I'd say FFXI players were the perfect choice for politicians.