Its Good to Talk !!!
Is it every a bad time to talk??
Actually yes there are times when its best to put it back
If you can't talk there and then though
Always arrange a time when you are free to talk things through
Don't let it be forgotten
I don't know about anyone else, but my children could and still can be very inventive at sidetracking me from bed times !!!!
It can be anything from discovering that piece of homework they thought they had already done, so offering you a foot massage because you look so tired.........oh yes very inventive 
But sometimes, they will go quiet at bedtime and ask "to talk"
it can be very difficult at this point to be discerning and realise what is more urgent
1)Their need to get a good night sleep
2)Their need to unbottle something that is really bothering them
What makes this even harder, is realising that what may be a huge problem to our child, is too small to worry about in our opinion, so we then have to look even deeper and see just how big a burden your child is actually carrying around
With my boys I go through the following steps
1) I tell them to give me the quick version of the problem
2) I ask a few questions about what they want the outcome to be
3) I make a decision !!!!
In most cases it is quickly clear to me that the issues they want to discuss, are not imperative to dig deeper at that particular moment
So I make an arrangement with them...
We decide on a time when they can have me completely to theirselves on a one to one basis, it can be anything from waking a little earlier in the morning, to first thing after school or a convenient time in the evening, once I make an arrangement, we stick to it !!!! (Unless something unforeseen happens naturally)
In the meantime I am able to tell them, that now the problem is in the open and I know about it, this releases them from a lot of stress and anxious worries, I remind them they can get a good night sleep now, because I am going to help them sort things out. It is very rare that this reassurance does not work, they are a lot calmer, they don't have to carry the whole weight of their worries, its easier on them because now the worst part is over..... I KNOW the problem, they have TOLD me !!!!
Talking through problems at bedtime with children is very rarely a good idea. It can leave them raw and hurting. Long and Lengthy discussions where you dig deep at their emotions is hardly a calming scenario for getting them to go to sleep.
But reassuring them that even though the problem is still there tomorrow but now you are going to help them, gives your child such an immense feeling of relief, that going to sleep is a natural side effect of that relief