As a general rule Miniatures are more hardy than their
larger brethern. This is due to most minis being on their
own roots and not having the fragile graft area.

For the most part a 48 hour period of 20F will put roses
into complete dormancy. If the temperature is fluctuating
sufficently they will also pop right back.

Containers don't provide the insulation of being in the
ground which will have a significant temperature moderating affect. Were I
to 'protect' container roses
the strategy I would choose is to insulate the containers
rather than the foliage. Depending on the variety, all roses
are hardy to below 32F, the variety determines the temperature at which the
natural anti-freeze will no longer
protect from frost/freeze damage. New growth is always more tender that
canes that have turned woody.

The location can also have a significant impact on short
term temperature extreems. If the pots are on the ground
there is a lot of buffering from the mass of the earth, on
the other hand if the pots are on an elevated surface there
is no insulation and the entire container is exposed.