Like so many of these issues, it usually comes down to how its handled at an individual parish (pastor, deacon, DRE, or whoever is "empowered to make the decision) and even this might not be “one size fits all.” At my parish, for example, the pastor pretty much leaves it up to the DRE to decide whether a person should participate in a full year of RCIA, attend only the RCIA sessions on the sacraments, or just meet one on one with a catechist for a time or two.
For what’s it worth, for someone in your situation, I think 30 minutes is a little on the light side but an hour or two of discussion and perhaps some reading on your own ought to be adequate preparation.