Before and during!
Finances are the number one cause of problems in a marriage.
Not only will a bad credit history limit the couple's ability to get mortgages, etc., it can also be an indication of a cavalier or irresponsible attitude toward keeping promises, which is what getting credit implies: I promise to pay this money back to you. And please everyone, don't jump all over me, I know that there are millions of reasons for bad credit, including medical disasters, layoffs, vengeful ex's, ID theft, the whole nine yards. That's why I said it * can * be an indication.
If someone cheerfully melts the plastic on a regular basis without thinking about how it's going to be paid for, and by whom, and what the final real cost of the purchases will be, that's a scary person to be involved with, IMO.
And if they think that this is either not important enough to share with you, or even worse, if they hide it from you, then yikes, there are going to be some really long Discussions on down the road.
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007