When blending two finished wines is
> there a time period that they should be together before bottling?

Marc,

You need to wait at least one month before you taste the blended wine.
2-3 months will be better. Try blending it in 375ml bottles for your
test, it will aged a bit faster in a smaller container and you will be
able to taste it twice at let say 2 months and maybe 4 months. It
will give you a good idea of what the blended wine will really taste
at around 6-8 months of ageing in 750 ml bottles.

Séb