When I do fresh frozen BHO, I make sure there is no moisture on the surface to ice over the trichomes and then cut it up in rough ~1/4" chuncks. I stuff those in the thermos and after freezing the butane and thermos to -18C/32F, I add the butane and soak the first time for 30 minutes to an hour, depending on how pristine I am trying to keep it. I pick up the remainder with a second soak after freezing again. I've never run it over a couple of hours total, but perhaps Jump can regale us with some of his longer soak experiences in the great frozen north country.
I pour through a Chenoise strainer purchased from Roses Restaurant Supply and a simple commercial coffee filter from the same place, for the first fast filtration.
If I need it prettier than that, I redissolve it in ethanol and after freezing the solution to -18C/0F, I filter it using a #1 Watmann vacuum filter (~17 micron), followed by a 0.2 micron syringe filter, which takes out everything, down through bacterial size. Those come off E-bay, or from American Scientific.