You can put the media from the HOB
into the canister if you like, to get rid of the HOB
right away. Even the biowheel, you can tear it into pieces (keeping it wet during the process) and put it in the canister that way. Any foam or biomedia in the HOB
can go into the canister.
If you elect not to do that, I'd give it 3 weeks or so of parallel usage.