I have used Saaz to dry hop a Belgian once and did not like it.
I would not use a bag, as hops work better when loose in the fermenter.
As for the time you want to dry hop, I would definitely not go for 10 days. Never did. For me 2-3 days works best and get the best out of hops. Anything more, does not really add anything and most times, for me, it dulls the aroma and flavours, extracting too much of a vegetal/tomato stalky flavour.