Try not to become too rigid about how long you would need to know someone before meeting them when you are using dating sites.
The length of time often depends on how the both of you have been corresponding.
You could meet someone on a dating site and end up having to take more time in getting to know that person before meeting them than someone else who may have started corresponding with someone on the dating site at the same time that you did.
Even though it may not seem like they have done much with their online dating accounts so far, it is still not a good sign that they signed up on dating sites to begin with.
This is someone that is trying to get away from something in the marriage.