Two minutes with clothes on
We timed the free part of all 123 series, and in a typical one it lasts 2:12. In that time you meet the characters, learn what is forbidden about them and see the first spark between them. Candy keeps these two episodes safe for work by design, swimsuits, towels and near misses included, so they show you the premise and nothing more.
Where it changes
Episode 3 is the turn in every series, however long it runs. In the five-episode titles that leaves three explicit episodes; in the longer ones, such as the fifteen-part Mona's Worst Enemy or the twenty-part YES MA'AM, the explicit stretch goes on much further. The free opening is about the same size either way, so a long series asks you to commit to more on the strength of the same two minutes.
How much is shown
That depends on the series, not on any setting. There is no choice between a covered and an uncovered version of an episode; each paid episode is simply what it is. Where we have rated a title for how far it goes, the score in the corner of its cover tells you, and the review says what to expect without describing it.
Choosing by the opening
If you want to know quickly whether a series is for you, choose one that gives you more to watch for free. Staycation with my fiancee's mother runs 2:50 before the paywall and Under the Boss 2:56, so both let the premise play out further than the typical opening. Recent releases are tighter, at about a minute an episode, and get to the paid part sooner.