I tend to try and steep mine for as long as possible. At the same time I am not convinced there is much change after 4 weeks in most instances!
4 weeks after bottling is a good starting point, especially for cigarette and single varietals, the pipe blends were not my cup of tea.
Cigars, my favourite type of juice for net.com, sometimes I think they change after 4 weeks, other days I am not convinced. What I can say is after 4-6 weeks I can really taste and enjoy the cigar flavours.
The past couple of days, having just finished over the previous batch which was over 4 months old, I have started on my latest cigar batch, it's now 8 weeks old, to me the differences are minimal if any.