There are two factors here for me; Time of day, and life circumstances.
My youngest is a little bit more sensitive before bed than during the day. I would have two very different conversations with him depending on this factor. If we discuss life and death before bed for too long or with many questions – I can see his brain working in overdrive instead of focusing on relaxing.
When I say life circumstances I am referring to a birth or death (or illness) that has occurred. Obviously a child may be more confused or sensitive during these times.