And to use a potion in itself, of course aware, spend an action or free action?
As far as I know, there are no more "free actions" (or at least that nomenclature is gone). The PHB's stance is definitely that it takes your normal action to use the potion or administer it.
I don't see anything in the Bard features that would allow administration of the potion as anything less than a standard, normal action.
As for the Rogue, a Cunning Action can only be used to Hide, Disengage, or Dash--basically speeding along actions a Rogue is already taking rather than granting an additional action. So again, no dice for the less-than-normal-action potion administration.
Unless there's a loophole I'm missing, it will take the full action.