I've done light cures just overnight all the time -- it's going to depend on your prep though. Should I ask how they felt when you took them out of the brine? You're at a weird temperature. You're too hot for cold smoking and too cold for warm smoking. I typically smoke at about 150-200* until the IT is 140* or so -- usually 2-4 hours.... or I cold smoke for a 3-4 hours. I've never done tuna.
Don't agree with not to worry about IT when hotsmoking fish. Fish is fish and it is done at 140 to 145 no matter how it is cooked. If grilling or in oven the exceptions would be fish like tuna or salmon which if cooked to 145 is overdone IMO. 125 is more in the range for these. This is based upon my experiences with smoking fish for a long time.