Depends on the seeds as well as the species. Any where from 10 days to two years.
Cold stratification is pretty much the same as for Sarracenia, the major difference is the size of the seeds. Stratify them in finely chopped live Sphagnum or LFS, moisten with most of the water squeezed out. Or in the pots themselves. Or a damp paper towel with most of the water pressed out. Seal them in a plastic bag making sure there is plenty of air and pop them into the refrigerator for at least 4 weeks.
Note that not all temperate Drosera seeds need cold stratification. Be sure to check each species and form/variety/location.
