double digestion time - (Nov/19/2008 )

i have to do double digestion of PCR products with BamHI and KpnI (fermentas).
they recommend bam Hi buffer for both with 2 fold excess of kpnI.
incubation is at 37 degree but time is what i dont know??/ can any one help.
also how to proceed- both enzs simultaneously or sequentially?

one more thing- for doing 3 piece ligation does dephophorylation required/recommended.

thanks a lot