What is the right time for seclusion? When is the right time for seclusion? When is the wrong time for seclusion? How much time should be spent in seclusion?
I practice with Triratna Buddhists so for us solitary retreats are seen as an important part of practice. So much so that if one wanted to become ordained (as many do) then the expectation is of at least one solitary retreat. So if I can have a go at your questions

Right Time

When you have been practicing for at least 6 months and have attended at least one group retreat

How much time

Depends. The people that I know usual do a week but many start off with a few days. Ultimately people can and do spend months on solitary

Wrong Time

I don't believe I've ever heard of anyone saying a wrong time except with the above caveats. I guess as ever you should kind to yourself on these things. Even though it is solitary it is  up to you how you spend the time. It doesn't have to be 8 hours meditation a day if that isn't appropriate for you at that point. Many people for instance have spent some of their time writing (about the dharma) and have found that beneficial for them at that point.

Confession

I have never been on solitary retreat so this is all second hand. I do believe it is a valuable practice though so would like to at some point.