There are so many things you need to look at with this question. The first question I would consider is what is your goal? More signups? More conversion to paid? Less work? Once you have set the goal you can then test it.

With out data but thinking what I have seen in the past I would say here is what the possible things are.

- Collect CC at signup - will reduce pure signups but will have a higher conversion after the 30 days - Don't collect CC at signup - more signups, but lower conversion as more tire kickers and missed emails about putting the CC in - Collect CC after signup at first login - maybe a blend of the two above