Most filter cleaners are some type of acid. That's how they dissolve the oils, gunk and especially the calcium buildup on the filter fabric if you have hard water. If you soak your filters, next time watch the bubbles rise from your filters after you dunk them. That's the acidic cleaner at work dissovling the calcium particles.
As expensive as filters are, I wouldn't chance soaking them that long and possibly ruining them.
-Sarge