The right time to seek out marital counseling is ANYtime you think you may need it. A couple does not even have to be in distress to work on their marriage. In fact, the optimal time to access counseling is when things are going well - problems do not exist or they are minimal. That being said, of course most couples find themselves in counseling as a last-ditch effort – problems are at their worst, or things have been on downward spiral for quite some time. If you are your partner can’t see eye to eye, one or both of you are unhappy, or, the D-word has come up silently or out loud- it is probably time to consider counseling.
You need marriage counseling when you find your relationship in a situation you cannot handle. The right time to seek help is before you start asking yourself "How we came to this moment" but any time is a good time to ask for help. Seeking marriage counseling is the wise thing to do when you have a situation.