Rueda contratiempo is not really a separate structure, but it may be used in combination with rueda structures. For example by dancing rueda combo with two circles, and one of them dancing rueda contratiempo.
Rueda contratiempo is a mix between son rueda and rueda de casino. Basically you dance regular rueda de casino, with figures from casino, and timing from son (contratiempo timing). In practice, when dancing rueda contratiempo you would commonly use the rueda figures that are closest to the son traditon, like plancha/borracho, tornillo, roedo, caminando figures, etc.
Contratiempo refers to the fact that the emphasis is on beat 2-4-6-8 in stead of 1-3-5-7 (also referred to as ‘a tiempo‘). The word ‘contratiempo‘ may be translated to ‘counter timing‘ og ‘off-beat‘.